Where to buy terran blueprints?

I'm curious, where exactly can I find and purchase terran blueprints? I've heard they're quite rare and valuable in the market, so I'm eager to know the most reliable sources to acquire them. Are there any specific online platforms, auction houses, or private collectors that specialize in these blueprints? Additionally, what factors should I consider when assessing the authenticity and value of terran blueprints to ensure I'm making a worthwhile investment?