I would get some Sennheiser PX-100 II and call it a day.
While they're not from the same era,they look just like the portable headphones from that era.so 99.5% of folks wont know they're not period correct for that walkman.
And they sound about as good as one can expect this sorta headphone to sound,plus they can fold up and be carried in the handy little bag they come in.
I know I really like mine,would buy another pair w/o hesitation if anything happened to those.
Only other ones I have like that are some el'cheapo TDK HP100 that I bought years ago to go w/my Zen Mosiac Mp3 player,and they're just about as good as the Senn's.
JM2¢ ~ FWIW
Bret P.