Some vpns support usually a single port forward but it can be restricted to certain servers and potentially tricky to set up. Others can answer better on individual providers.
But just to correct a common misconception, port forwarding has nothing to do with seeding vs leeching. Port forwarding is so that you are connectable (others can connect to you). Two peers that are not connectable cannot connect to each other, but as long as one is connectable then a connection can be made and data can be uploaded/downloaded between the two.
So not being connectable will reduce the number of peers you can connect to, which will only really be an issue on torrents with few peers