Where do I start to look for an apartment for my stepdad?

My stepdad is 75 yrs old. He lives by himself now since mom passed away and his biological children are married and have their own families. We all didn't have a good relationship with him so we don't want to live with him but he needs to move out of the house and into an apartment he can afford. Where do I look for special apartments for him? 55plus communities?