Hello funinabottle and a Big welcome to the forum.
There's an excellent website from a very known swedish collector, Ulf Buxrud, who also collects the Rare Malts Serie. There's a load of different bottlings, packages and editions so you better be prepared to spend some money if you're after them all.
I suggest you check it out. It has some invaluable information.
Most of the distilleries owned by Diageo also have large selections of the RM Series so if you don't find what you're looking for at your local store or webshop you can always try there.
This is the Ulf Buxrud Site:
Cheers and happy hunting...