I don't have the number for Weaver bases but I use Warne "Weaver" style steel bases on my model 21 Cooper. I do not have the number for them but you can look them up on Warne's web-site or give a call at their 1-800 number and they will supply the info.
I certainly would not have any qualms about using Weaver's if they do indeed make them for model 21's.
John, I know you said Weaver bases. Talley lists a real nice set of rings and bases for the Cooper. You might want to look at them. I used leupold on my Cooper. The Talley were nicer and lighter.
Steve
I got my last set of Warnes thru Lock, Stock & Barrel, they had them drop shipped to me from Warne, I had them in just a few days.
LS&B does have a website and if you want to talk to a real person their 800 number is listed on the website page, and they are good people to deal with.