You can google online, there are many stores offer bifocals. My last pair was bought from Firmoo, cost me only $30 with the bifocal lenses and the shipping, quite afforfable and it got lots of compliment from my colleagues and friends! Worth trying, check out at https://www.firmoo.com/bifocal-glasses.html.
I know many online optical stores sell bifocals and they also have great customer service which can help you to get a pair of bifocal glasses according to your needs. I know one that is Firmoo.com which is an online optical store and can provide you with cheap and good bifocal glasses.