At the risk of shameless self-promotion, I've placed a GPIB-to-USB adapter on the E-place for sale/auction. I hope I've chosen a reasonable price range.
If you want to have a look, it's item 150972490568.
Keep the peace(es).
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Bruce Lane, Owner & Head Hardware Heavy,
Blue Feather Technologies --
kyrrin (at) bluefeathertech do/t c=o=m
"Quid Malmborg in Plano..."
Bruce Lane