As you already said, sadly the DMGuild is very restrictive on new settings being pubblished so that's not an option.
Honestly beside your official site or Drivethrurpg I don't think there are many other platforms in which you can reliably share the PDF. Ofc Kickstarter can be an option as a sort of preview or quickstart rules document, but I suspect that you will wait after the trial baloon is released and how is it well received to decide about going full on the project.
But I know some fairly frequented subreddits (for example r/dndnext) and forums (Giant in the Playground) about D&D, in which you can share the link for Drivethrurpg or your site (especially if it's a Pay as you Want or free document) to better spread the news about Symbaroum 5e ruleset and better evaluate the community reactions. Also the EnWorld site write a lot of articles about news on rpgs and I think they would be interested about a possible 5e ruleset for Symbaroum if you let them know about it. I will surely post the link to the "trial baloon" on several of the above sites once you release it, because I wanted to spread the knowledge and love for the Symbaroum game, which I really, really like.
Also, I know a lot of people which are fascinated by Symbaroum as a setting (people are sick tired of the Forgotten Realms ahahahah) but are not interested in the game system (mostly for lazyness tbh), so based on my personal experience I think that the trial baloon, with a little "marketing" done right, can be really good for the game as a whole.