The photo is a little dark, but are your current pin-posts welded or bolted onto the trailer frame?
I did this years ago when I had the pin-post like you did, but purchased a Yamaha Waverunner that had not bow eye for the pin post. So you can purchase the entire winch post with winch that bolts onto your trailer frame. I can't tell you if they would work on yours as it is too dark to see.
Any trailer shop could sell you a winch post. Or you may be able to find it online at like E-trailer.
Good luck!