Here is my solution:

LINK 800
GRAB 200
LINK -1
REPL SAVER
MARK INC_X
ADDI X 1 X
MODI X 10 T
FJMP MUL
COPY X #N2KW
TEST F > #N2KW
SEEK -1
TJMP INC_X
TEST F = #N2KW
SEEK -1
TJMP FOUND
MARK MUL
SUBI X 1 X
MULI X 10 X
COPY X #N2KW
TEST F = #N2KW
SEEK -1
FJMP INC_X
MARK FOUND
COPY X M
VOID F
COPY 0 X
TEST EOF
FJMP INC_X
COPY 0 M
MARK RECEIVE
COPY M F
JUMP RECEIVE

MARK SAVER
MAKE
MARK SAVE
COPY M T
FJMP SAVE_END
SEEK -9999
COPY T X
MARK NEXT
TEST EOF
TJMP APPEND
TEST X > F
TJMP NEXT
SEEK -1
COPY F T
SEEK -1
COPY X F
COPY T X
JUMP NEXT
MARK APPEND
COPY X F
JUMP SAVE
MARK SAVE_END
SEEK -9999
MARK SND
COPY F #N2KW
COPY #N2KW M
TEST EOF
FJMP SND
WIPE
KILL
GRAB 200
LINK 800

seem to be having a problem were testing for #N2KW < F is giving wrong results, for example when i test 6666 < 32 it says true and we all know that 6666 is not less than 32. anyone else ever have a similar problem?

Really nice puzzle. Took me quite some time to figure it out.