I used to get generic V in Mexico, which is available in every single pharmacy still. It had varying effectiveness, as likely also those other mail order ones that's prevalent now, due to lack of FDA oversight on the overseas manufacturers.
I just get it from my US doctor now. I know the OP (from over a year ago) said he couldn't get it from his doc because he didn't need it. If that's the case, just tell your doc a little white lie and say you do. It's not like he'll have a test for you and send in his hottie medical assistant and see if you get hard. Your doc will just prescribe it and you use it as needed. You fill that prescription as frequently or infrequently as you need. I currently keep a 16-24 dose supply and order as needed through Kaiser. With these I know I'm getting the mg's that's listed on there.