There are a growing number of Telegram groups dedicated to helping Windows phone fans. Starting with this one and (here) a new group for WP8.1 users who would like to root their phones and sideload applications. Links to unencrypted 'xap' files are included in the group - just be aware that all of this is extremely unofficial and that if things go wrong then you're on your own!

From the group's founder:

Since I introduced the W10M group to new users, I've gotten PMs in Telegram, Disqus, and also in Reddit that it will be good if there is a also a xap collection where people can download unencrypted xaps without searching the net for random files.

So I started a WP8.1 group (W10M and WP8.1 groups are connected to each other, you can see from group descriptions) a week or 2 ago and now it has 103 members, so it seems it's growing fast.

As a help to new ones, I have written a lot of possible questions, with answers, and also penned a tutorial on how sideloading is possible again in 8.1. I've pinned them permanently, and also uploaded the xaps I have to the group. 

Here’s the invitation link :- https://t.me/W8Mobile

Good stuff. Most platforms seem to evolve an enthusiast file-and-expertise sharing system or two after official support wanes.

PS. If you're wondering how to access this new Telegram group on Windows phones, for 8.1 I think the official Telegram app still works, once side-loaded, while there's Unigram Mobile Messenger for Windows 10 Mobile.