There are work camps, staffed by prisoners of war or criminals in various nations, but these will also be somewhat protected.

Now it is true that both of these groups and indeed others like the Ordanans who have teams of talented alchemists do tend to want to maintain thier monopolies on alchemical products, and so wouldn't be willing to let a prospective master alchemist just wander anywhere there are better prospects. However even there you run in to the issue of your island being less appealing than most.

However, the task of refining the Saltpetre in to a form worth selling is less demmanding than that of making the end products they buy it for. If you're willing to settle for the second, you have a broader range of targets. From the undercity of Ordana, to Clan Marwolaeth in the beastclans. You used to have some in Marcelia, but they were all killed or fled during the course of the civil war, or else are going to be in the capital and better protected than elsewhere. It's an unusual enough skill level that you won't just be able to recruit one, but most courts in the land will have one you could take, and there might be a few private or criminal enterprises with them as well.