GoutPal has a purine content list which seems standardized per weight. You could convert those values into whatever serving sizes you like to use but I don’t think there would be much point because there is no particular amount of purines you should be eating in the first place. Purines aren’t like proteins or what have you in that the ideal amount in your diet is simply zero. But of course you need to eat some.
My assumption would be that if you’re told to go on a low purine diet that simply means you ought to try eating less purines. And for that purpose, even if you wanted to bother with counting purines the amount per serving wouldn’t be useful. What you might be able to make use of instead is the amount of purines per calorie or relative to the amount of protein in the food.
Realistically though, the practical way to achieve a low purine diet is simply to avoid the especially purine-rich foods. The difference between the purine content of cheese and meat for instance is so large that the actual values don’t matter: if you have no reason to avoid dairy (lowering the amount of purines you eat ought not to be your only dietary concern!), getting most of your protein from dairy is the easy ticket to a low purine diet. It can be that simple.
Most of the plants containing little protein also do not contain much in the way of purines so you can eat your fill of that stuff without counting purines.
In addition to limiting purines, noteworthy among the things which might help you lose some uric acid are:
-eating enough vegetables containing lots of magnesium, potassium and calcium to help your body get rid of the uric acid it produces
-limiting fructose, especially when used as a sweetener (see HFCS)
-losing weight (if applicable)