Does anyone know of a place to get vinyl record covers?

You have a few options, depending on what you want / the sleeves you want.

Firstly, you can pick up copies of most old albums (Queen included) for a few coins online / charity shops. Of course, some might be tatty, but that lived in look can be nice. Yes, you'll have a spare bit of vinyl, but thems the breaks, right? A shop like HMV will do LP sized prints / canvases, but I've noticed a lot of these are cropped badly.

If you want something a little more special, on eBay you can usually find old shop display 12" x !2" covers - usually used as ceiling mobiles or counter displays. Some can be expensive, but again, depends on the album. 

A better option for something more valuable or to have a mint image is just to find the sleeve online (google search with 'large' ticked) and find the best option for you. Use these to order 12" x 12" prints from your local store. Doing it online is also a good option, most supermarkets will offer this service. I've had some good results from bog standard 1200 x 1200 pixel images but these days you can find huge versions online. Once it's in a standard LP frame, it will look great, especially when on the wall and away from up close inspection if they look a bit ropey.

When sending off to an online company, a nice tip is to pump up the resolution to 300 (most online images are at 72 I think) and change the physical size to something over 50cm x 50cm. This will trick their printing computer into thinking it's a good quality image suitable for a 12 x 12 print. If you know your way around Adobe, you'll know what to do.

Another nice tip doing it this way is to get the back sleeve too and have them side by side on the wall.

Not so far, fingers crossed!