here is a spreadsheet of various websites that have been programmatically found to accept guest posts (via pattern matching etc). The data is a by-product of a different project I've been working on, so here is a subset of 1000 entries for all forum users to use for whatever they wish.
The data given is as follows:
Domain, Language, Guest Posts URL, Contact URL, Broad Category
Domain - the domain name
Language - extracted IETF language tag (eg. en-US for US English)
Guest Posts URL - url identified with either guest post details or list of guest posts
Contact URL - url identified as a contact page/form
Broad Category - a broad category for the site, determined by an API
All the data is checked via scripting only - I haven't hand checked them all! Some outliers may be present, and the freshness of the data is currently 30 days max at time of posting. YMMV
What can you do with this data? Some ideas:
1) Enrich the data - Run the list through your favorite APIs to check for traffic, RDs, domain age, even 3rd party metrics if you really want.
2) Find sites in your niche via keywords in the domain. Check out the guest post url for these sites and see what the procedure/cost for a guest post is.
3) Blacklist the entire set of domains from your link-building prospects, as they're far too easy to identify as being a site that sells guest posts!