I'm getting older and like warm things now. Who sells a heated cab or has plans so I may make it?
Do a forum search and you can find a number of options. There's essentially a few different cab options available in the US/Canada from Laurin, Sims, Jodale Perry, and Curtis. The Curtis cab is probably your cheapest option. (If you're based in Europe, then other options exist.)
Here's a good starting thread with pictures of several of the cabs installed on the BX2350:
http://www.tractorbynet.com/forums/kubota-owning-operating/114242-bx2350-24-laurin-cab.html