I don't think you are likely to get an answer. You are replying to 2 1/2 year old posting. Soontobecruiser hasn't posted anything else at Sailnet since 2010.
You could try posting your question in the Gear and Maintenance board along with a couple of pictures that show the square hole and a measurement of the square hole.
Alternatively, you can try some of the marine consignment shops around the country. A large number of them have been discussed on these boards over the years. To find the Sailnet postings containing them, use Google and enter search terms site:sailnet.com consignment.
As you talk with the consignment shops, keep an open mind about possible solutions. Personally, I should think that you might be better served in the long term by replacing the oddball winches. If you aren't looking for the self tailing variety, used ones are available at very reasonable prices.
I will mention Bacon Sails
specifically because I am familiar with them and they are close by. The other guys are undoubtedly just as good. Bacon's has a huge inventory. Their web site shows some of the stuff they have, but calling tends to produce better results. Their phone number is 410-263-4880. They get calls from all over the world and ship stuff so you don't need to visit in person. BTW, I have no relationship with Bacon's other than as a customer.
When I was in there last week buying some stuff I noticed they also sell a rubbery device you can put on non-self tailers to turn them into self-tailing winches of sorts (they feature line grippers but no line stripper piece). I don't have any experience with them so I can't speak to how well they work, but they are inexpensive and might be worth an experiment. Maybe someone who knows them better could comment?