It is important to note a few things about the filters on the trade opportunities page.
1.) Every filter is an AND, not an OR. So if you put in both Rhystic Study, and Aura Shards, you will only see the users that want BOTH cards, not all users that want EITHER card. Similarly, if you put in a specific card that you are looking for, it will only show you a user that both has that card, and wants Rhystic Study. As such I almost never use both on the same search. Also be mindful of the other search criteria at the top of the page. The defaults are generally ok on those, but sometimes I'll drop the minimum of 5 feedback filter to pick up a couple extra options.
2.) The search is not particularly intelligent when it comes to versions of cards. If you specify, for example, the prophecy version (default) it will only show users that have specified the Prophecy version in their wishlist. It will not show users that don't have a version specified. As such, when I just changed from Prophecy Rhystic Study, to unknown version Rhystic Study, my opportunities just jumped from 11, to 3 pages. That said, specifying unknown version will show all users that have any version of the card, so you will need to check each user that appears on this search, and make sure they don't have the Commander's Arsenal version specified. (I just quickly did that search, and only 5 users appeared, so most of those 3 pages don't have a version specified.) Not particularly relevant for a card that's only been printed twice, but could be significant for a version that has a dozen printings.
Hope that helps!