Converting 3 handle to 1 handle in shower/tub

Hi, Need to find out where one can get at "conversion" plate that will cover existing holes for 2 faucets when I replace it with one. I own a resort and it is now required by a new code to have the "mix" of hot and cold water so guests will not scald themselves. Any suggestions where to find them? Thanks so much!

Often called a "remodeling plate",they are available at the plumbing supply house.Best case scenario,you should be able to get one made by the same manufacturer as your replacement faucet.One example is the Moen 1920.

Delta's is an RP29827 in Chrome and the list price is $23.05

Thanks so much for the info. I have Moen faucets so I will check out the availability in my area. THANKS!