Hi Kate,
Welcome to the forum.
With BBQ supplies stores i find myself buying from all over the place just to find the exact thing that i'm looking for at a particular time.
For a thermometer i'd say you can't go wrong with a Maverick ET-73 as this will do both you smoker and meat temp's. You can get them for about £50.
For charcoal most people on here will get it from a local cash & carry and get resturant grade lump wood charcoal, so if you've not got a card you might need to sweet talk a friend that does. If you can't which i can't from time to time i find myself trawling the garden centers (but be cafefull if they've been leaving them outside over winter) or i've found my local Go Outdoors store keeps loads of lumpwood charcoal even over winter and it's all kept inside.
For the rib rack i got a weber one from
www.bbqworld.co.uk and they also do beer can chicken holders (but i just use a beer can or a coke can with some holes in the side and they stand up fine like this). and i've been getting the weber smoking woods from here too. I think one of the site sponsors also has a constant supply of woods which are supposed to be good also.
Other than that get freindly with your local butcher, and have fun.
Thanks,
Ed