I want to buy a new nut and a new bridge saddle. Is there a website that has those specific parts for the Epiphone Dove?
Usually you don't have to worry about brand-specific replacement nuts and saddles. Just measure your guitar, or check your specs. You'll need to know the nut width, the string spacing at the saddle and whether your fretboard is radiused. It's a good chance for you to upgrade too. You can buy those parts anywhere -- if you're not sure, take it to the shop with you when you buy, or call Epiphone and ask them for the measurements.
Typically, you would have to have these items made by a qualified luthier who will shape them from blanks, and usually would include a set up and possibly fret crown & polish with the new nut & saddle. There are several materials you can specify; bone, ivory, tusq, etc. Probably the best sounding and most cost-effective for your epi would be tusq.

You could try to make these yourself, but its very tricky work and it can throw your intonation and action way off if you do it wrong.
I'd recommend taking the opportunity to have bone ones fitted, at this stage.

You'll notice a big difference in sound.
Sincerely, Chad.
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I just ordered a new Tusq nut and saddle, hopefully they'll do some good.