Hi I play lotr lcg quite a bit with my wife and kids and just love it to death.

I would really like to get the gen on and fellowship promos since this is my favorite game of all time and has done so much for me and my family enjoyment that I now feel like I need to try and get some of these!

Alt art cards and the pre-order promo cards might be difficult to find here, you will better off in the facebook group and Ebay, where sometimes those cards are offered up. Playmats can also be found there, but you will have to get lucky and find someone willing to part with their items. For a full list of the items, see this article: https://visionofthepalantir.com/2019/12/14/collectables-in-lotr-lcg/ It als provides some tips when searching for the cards and mats, but it will involve a bit of luck and some deep pockets.
Good luck with your search