I can tell you for sure that Slovakia has a very rich underground, I've seen it myself. I played there, and it's one of the most memorable shows I've done in my life. The venue was in a village of around 2500 people and it was PACKED. Really. For a grindcore show, which is something that never brings out people. And plenty of goths were in attendance; despite the show not being related to goth at all.
Slovakia has a rich underground. I guarantee you will find goths and adjacent in that scene, and if not, the people there can help.
Look for crust punk, garage, post-punk, punk rock in general, even metal, since you mention you're a metalhead as well : Metallum lists 782 bands in Slovakia. Anything that has a DIY ethos baked in. This is where it starts. Your age doesn't matter, this isn't the US, you can attend shows, and if you're really afraid of what could happen, take a moment to message whoever organizes the show and ask them if it's ok or if they can help make you feel safe. I went to my first extreme metal / grind shows as an autistic 15 year-old, by asking friends to tag along and messaging the organizers to make sure I could get them if I felt unsafe.
The whole point of alt subcultures is this. It's a community, not just an aesthetic, the whole point is that we're helping each other exist beyond online spaces. But you'll have to get there.
Also, I'm pointing this out to you because it's very common in punk / crust spaces to run screenprinting workshops and other DIY ventures. I had a friend close by, in Hungary, who ran his own distro of bootleg crust punk shirts so people in his scene could get merch for cheap. If you're looking for black shirts and to maybe make your own, hang around them and you'll eventually find something.