Where can I purchase a custom dog bed cover?

Anyone that sews can whip one up pretty quickly. The fabric stores have cutting tables, go there and ask if they have a book of local sewers who do work. All the JoAnn Fabric stores have business cards in a binder for that.

Try Etsy or other crafting websites.

Look at local craft fairs for someone who can make something custom for you.

Consider a local tailor or other garment maker.

Any person who does custom garment sewing should have the skills you need to make a bed cover for you.

You could also try. You can get sewing machines pretty cheap, and fabric stores are always having sales on fabric. You could try making a bed cover, so if your dog does something to the cover you ca easily make a new one rather than having to spend another couple of hundred on making a custom one.

Yes, a few hundred is what I estimate this to cost you. You have a dog bed the size of a mattress. That won't be cheap.

they have websites where you can purchase custom things, my brother does, google