They stopped making them about 25-30 years ago, but , they are pretty easily found on the internet .If you look on E-bay for example you can usually find about a hundred on there at any given moment, some even new in the box . Prices range from $ 25-$ 75 depending on the brand ,the number of bidders, etc.
With original FM radios going for anywhere from $ 200- $ 1,000 or more(depending on year/make/model)
and having your AM radio converted to FM costing in the $ 450 range ,
These old vintage FM converters are Without a doubt ,the cheapest way to get FM .

Greg