You should check some of the UKAPS sponsors websites.
I've used @Aquarium Gardens and the plants were great. Ebay also has some good sellers.
I can't find anywhere around Manchester to get plants apart from the abyss in stockport. All the LFS sell basic stuff. Pets at home do some tropica plants but vary per store, the bury store had some nice growing tropica but others are terrible. They get stock in on a Thursday I've been told.
Im in need to buy plants for my new setup and may just order from https://www.aquasabi.com. Aquarium Gardens don't seem to do much 1-2 grow carpets
Yeah my local pets at home is one of the better ones admittedly but still lacks the likes of limnophilia atomatica, blyxa and some others I wish to try.
The abyss does sound tempting. I might head in that direction at weekend as its only 10mins on the motorway.