For an RV....Walmart.
Take the old one out, measure the opening. Walmart has a couple of small (dorm room) style ones that will probably work.
They are harder to replace if yours is vented to the outside, most RV ones aren't - just plug and play.
"If we couldn't laugh we would all go insane."
Arctic Fox 25Y
GMC Duramax
Blue Ox SwayPro