The requirements you mostly need to meet are “constant current driver 700 mA” and “dimmable” with an output very close to the maximum listed for the original. You can buy them on eBay for well under $20. Here’s one for $12 and with 38W - https://www.ebay.com/itm/Magtech-M38-U54-0700-XP-38w-700ma-constant-current-LED-driver-dimmable-freeship/253938710629?hash=item3b1fed3865:g:uQIAAOSw8fJbn8uj:rk:2:pf:0
39W for LEDs is a lot of light for a fan. Are you sure they didn’t build in a bit of slop for the driver? The electronics are the obvious weak point in LED lighting since the LEDs themselves are rated for 50,000 hours if driven at the right voltage.