as superuser:

create or replace function bytea_import(p_path text, p_result out bytea) 
                   language plpgsql as $$
declare
  l_oid oid;
begin
  select lo_import(p_path) into l_oid;
  select lo_get(l_oid) INTO p_result;
  perform lo_unlink(l_oid);
end;$$;

lo_get was introduced in 9.4 so for older versions you would need:

create or replace function bytea_import(p_path text, p_result out bytea) 
                   language plpgsql as $$
declare
  l_oid oid;
  r record;
begin
  p_result := '';
  select lo_import(p_path) into l_oid;
  for r in ( select data 
             from pg_largeobject 
             where loid = l_oid 
             order by pageno ) loop
    p_result = p_result || r.data;
  end loop;
  perform lo_unlink(l_oid);
end;$$;

then:

insert into my_table(bytea_data) select bytea_import('/my/file.name');

Here is a general way of getting a table with bytea data from postgres into a similar Oracle table with a blob.

It should be trivial to adapt my test to your real tables, and you should probably increase the size of the 'chunks' that I used to keep the output readable, from 20 to something more like the 2000 limit for string literals (4000/2 as each byte is 2 bytes hex).

1) postgres
testbed:

begin;
set role dba;
create role stack;
grant stack to dba;
create schema authorization stack;
set role stack;
--
create function random_bytea(p_length in integer)
       returns bytea language plpgsql set search_path to 'stack' as $$
declare
  o bytea := '';
begin 
  for i in 1..p_length loop
    o := o||decode(lpad(to_hex(width_bucket(random(), 0, 1, 256)-1),2,'0'), 'hex');
  end loop;
  return o;
end;$$;
--
create function bytea_to_oracle_sql(p_id in integer, p_data in bytea)
       returns text language plpgsql set search_path to 'stack' as $$
declare
  o text := 'insert into foo(id, bar) values('||p_id||', empty_blob());';
begin 
  for i in 0..(length(p_data)-1)/20 loop
    o := o||chr(10)||'update foo set bar=append_to_blob(bar,'''
          ||encode(substr(p_data,i*20+1,20),'hex')||''') where id='||p_id||';';
  end loop;
  return o;
end;$$;
--
create table foo(id serial, bar bytea);

insert test data and check hashes:

insert into foo(bar) values(random_bytea(90));
insert into foo(bar) values(random_bytea(90));
select id, md5(bar) from foo;
/*
 id |               md5
----+----------------------------------
  1 | 32a24c8827047eff517e8a40bf3ad8b4
  2 | 25ac852000889ab782ad6437accf1546
*/

generate Oracle script:

\o '/tmp/oracle.sql'
select bytea_to_oracle_sql(id, bar) from foo;
\o

contents of /tmp/oracle.sql:

insert into foo(id, bar) values(1, empty_blob());
update foo set bar=append_to_blob(bar,'ddbe858f7905551862507ddaa3b5410cba8013d4') where id=1;
update foo set bar=append_to_blob(bar,'089d6e66f16b10ba1204a4efc22a7f3c2fd45492') where id=1;
update foo set bar=append_to_blob(bar,'24d26dc887afd4412fe8163786859e77f0af3202') where id=1;
update foo set bar=append_to_blob(bar,'b3d7f2750172b2314606c36bd8313360e008a20f') where id=1;
update foo set bar=append_to_blob(bar,'f0b847763de6ee2e9521') where id=1;
insert into foo(id, bar) values(2, empty_blob());
update foo set bar=append_to_blob(bar,'3148f823befa95712bdc77ef4750207bb0018352') where id=2;
update foo set bar=append_to_blob(bar,'10730b58ea483ed876d4faa81df3ccdbed624d18') where id=2;
update foo set bar=append_to_blob(bar,'3ec40886142901c52a85173bf92393e36bd2bce2') where id=2;
update foo set bar=append_to_blob(bar,'a6b68ac3a9569f97b8ecaff7b1b87dc6e17f8b0b') where id=2;
update foo set bar=append_to_blob(bar,'04a347fdc6dae132ad9d') where id=2;

remove testbed:

rollback;

2) Oracle testbed:

create table foo(id integer, bar blob);
--
create or replace
function append_to_blob(p_data in blob, p_append_hex in varchar) return blob is
  o blob;
begin
  dbms_lob.createtemporary(o, TRUE);
  dbms_lob.append(o, p_data);
  dbms_lob.writeappend(o, length(p_append_hex)/2, hextoraw(p_append_hex));
  return o;
end;
/

run script:

insert into foo(id, bar) values(1, empty_blob());
update foo set bar=append_to_blob(bar,'ddbe858f7905551862507ddaa3b5410cba8013d4') where id=1
...

check hashes:

select id, dbms_crypto.hash(bar,2) from foo;
/*
 ID DBMS_CRYPTO.HASH(BAR,2)         
--- --------------------------------
  1 32A24C8827047EFF517E8A40BF3AD8B4
  2 25AC852000889AB782AD6437ACCF1546
*/

_{credit to Vincent Malgrat for his concat_blob function I adapted. See here for the random bytea function by itself}