Minolta number ACW 100.The fitting is 49mm. The item is no longer manufactured by Komica Minolta.
A compatable lens by another manufacturer would do. Check the below links for some of the ACW-100 adapters I found online. I would recommend calling ahead to make sure they really have them in stock!
There is also one on Ebay, and if you keep looking, you will probably find more on Ebay... Also, if you search for "minolta a2 wide angle" on Ebay you will get a few more hits on non-Minolta wide angle converters. Some of them quite cheap, not sure about the quality though.
The last link is to a non-Minolta maker called Raynox. It's 49mm but I'm not sure how well it would match your A2. This one is more wide angle than the ACW-100. | 