If you wanted f/m western erotica, a number of the specialty romance publishers give some away free on their websites (may be price-matched in other stores).
Samhain Publishing offers a short story in Lorelei James' f/m cowboy series:
Slow Ride About twice a month, they offer freebie novels from their imprint, some of which are occasionally westerns.
Ellora's Cave offer
free read short stories across multiple subgenres and some weekly rotating longer works. They also have a Values from the Vault section where they sell older titles for $0.99-$1.99 and here's what shows up under their
dedicated "Lawless" imprint for cowboy westerns, although there will be some other westerns not under that imprint in other sections as well.
Pink Petal Books have a couple of
freebie short stories on their website, both f/m and m/m.
You can also look through All Romance eBooks'
Free Reads section to see what they have. A lot of it is self-published, though.
If you're okay with self-published stuff, a lot of new and formerly traditionally-published authors upload things to Smashwords, often for free. Here's what's under their "
western erotica" tag, although you're bound to find even more by just browsing the general categories or doing a keyword search.
Hope this helps and welcome to MobileRead!