Easiest way to find the RSS feed on most sites is to search for "RSS" in the page source; there's usually just one instance, and it's a direct link.
These days, many sites don't advertise their feeds, but it's still in the source (and is often broken in one way or another). If it is botched, a friendly email to their web admin with a link to the W3C Feed Validator [1] can go a long way; most times it's an easy fix for them.
That works for the main firehose feed and https://news.ycombinator.com/showrss, but there isn't a feed for the ask posts as of yet that I've seen anyway.
