QuasarMX [1][2]is available to users in three versions: Lite, Pro and Pro beta/pre-release. The first level is free with restricted functionality, whilst the latter versions require a payment on the author's website via Paypal.

The Lite version can be found on OpenRepos, while paid versions can be downloaded from the author's servers (authentication is required to access).

I'm not sure what Jolla's intentions to paid software is, if they have nothing concrete, maybe it would be worth approaching them with a proposal for a cross-platform store. If they're not interested, then maybe OpenRepos as others have mentioned. Aaron Seigo and others worked on an open sourced software store called Bodega [3],[4] as part of the doomed Vivaldi project, this could find use here.

[1] http://talk.maemo.org/showthread.php?t=81318
[2] https://www.meteorasoftworks.com/quasarmx/buy/
[3] http://aseigo.blogspot.co.uk/2013/10...ticipants.html
[4] http://quickgit.kde.org/?p=bodega-server.git