Who sells greater soul gems?

Excuse me, I was wondering if you could provide me with some insight into the market for greater soul gems. Specifically, I'm interested in knowing which vendors or sellers typically offer the best deals or the largest selection of these rare and valuable items. Are there any particular merchants or marketplaces that you would recommend exploring for someone looking to acquire greater soul gems? Additionally, are there any factors I should be aware of when evaluating potential sellers, such as reputation, pricing, or quality control measures? I'd appreciate any information you can offer to help me navigate this specialized market.