It's a darn good time to be a UI/UX designer who wants to work from home

Most of the ones I've seen just scrape other job sites or feeds, like Monster or Indeed. Standalone ones are going to provide higher quality listings, like:

Authentic Jobs, although you have to provide search terms: https://authenticjobs.com/#onlyremote=1&search=ux%20or%20ui%...

We Work Remotely, formerly the 37signals job board: https://weworkremotely.com/categories/1/jobs

Slack at Work, for companies that use Slack, although you seem to have to search for terms one at a time: http://slackatwork.com/