Hi --
Welcome to the Forum!
Unfortunately, none of Yamaha's current keyboards use this type of expansion module anymore. Nor will they be used in the future, and I doubt if they are being made.
You will probably need to search the second hand (used) market like eBay or whatever. These modules were also used some earlier Tyros models and in Motif XF. The Yamaha model names are FL512M and FL1024M. Only Mutec made a 2GB module, if I recall correctly. I suggest searching on all of these names.
I saw a few modules on eBay and Reverb.com with a wide range of prices. I would definitely be careful as some sellers have jacked up prices beyond reason.
Wishing you good luck -- pj