There are no Volvo seals, they buy them from manufacturers of seals and stuff them in a plastic bag with a Volvo part number. The suppliers change throughout the years as well. Saildrive ones were from Stefa for a while.
So you just pick one with the right specs (size, material, stainless spring), which is what usually keypart/parts4engines do for you if you can't be bothered to do it yourself. Plenty of of online seal dealers around. Back when I needed one, they happily swapped the spring for a stainless one on request.