So my friend has been wanting to find more online places to buy vinyl albums, but I'm not sure myself of where I would buy vinyl albums myself. Are there any websites that have dedicated places to buy them?

There are a few. I'm a vinyl enthusiast myself, and I know plenty of shops still sell them. Any shop that sells older (i.e. vintage) merch will carry vinyls. Even most music stores still seem to keep a stock of them. However, here are a few I know of:

https://lp.reverb.com/

https://www.barnesandnoble.com/b/vinyl-albums/_/N-1p2a

https://www.recordstore.co.uk/

https://www.vinyltap.co.uk/

I haven't bought any online in a bit, when I do buy vinyl, I usually go to a local shop.

One place that's still around I've used is https://www.dustygroove.com

eBay is actually pretty good for vinyl, a lot of actual record stores sell on there. Discogs has a lot, though I mostly use their site for reference, but recently a friend who buys a lot of vinyl talked about buying from there.

Googling what you want will usually take you to a cool place that has lots of other stuff you'll want, so throw a few titles in with "LP" and/or "vinyl" and you'll probably find a few places that sell to your niche.

Discogs

vinyl-digital is a good shop overseas that has basically everything. Caveat is shipping, but for vinyl you can't get in the states it's really good. otherwise I follow some of the reddit threads, vinyldeals, vinylcollectors, where people will post deals or sell/trade their own vinyl. Have found some really great deals that way. vinyldeals usually posts items from amazon, reverb, walmart, and ebay, but there are some other sites as well that come up