Tom,
These are just my thoughts hopefully you will find something useful but please keep in mind that I have no experience in the firearms industry...
Based on the two manufactures you currently distribute; Rohrbaugh and Seecamp, you could look at your business in two ways: 1) A dealer specializing in small carry pistols, or 2) A dealer specializing in high end / difficult to find at your local gun shop pocket pistols.
Depending on which way you see your business there would be natural ways to expand, each with its own set of positives and negatives.
If you would like to build up the business based on carrying small pocket pistols (scenario #1) a natural extension would be to start offering guns like the LCP, DB9, P3AT, Kahr, etc at various price points. One of the largest negatives with trying to expand this way would be that you have already built a strong customer base for the higher end/harder to find pocket guns and I suspect you would have a difficult time leveraging your current customers for the lower end guns, I’m sure there would be some but most of the folks who carry an R9 do not have much of a need for a DB9 etc. I also suspect that the volume required to make the lower end firearms attractive you would have to capture quite a few new customers and as you know there is a cost associated with each new customer acquisition (time on forums, advertising banners etc.) so if you can it is best to try to leverage current customers as much as possible. The last negative I can think of specific to distributing the lower end firearms is that they are more commoditized and are for the most part available at peoples local guns stores, so it may be harder to justify paying a $25-$50 FFL transfer fee on a $300 gun where many willingly pay it on a hard to find $1200 R9. One positive I can think of is that once you do capture some of the lower end consumers those same buyers may become repeat buyers as they work their way up to R9s and Seecamps.
Things look better (IMHO) if you look at your business and decide to focus on expanding your higher end offerings (scenario #2). I think the Heizer Defense suggestion Ljutic made was a really good one, they are hard to find, different enough from your current offerings that you will be able to leverage your current customers, and fairly pricey so hopefully the volume you would have to move would be reasonable. A visit to your website also reviled this sort of mission statement: A licensed firearms dealer since 1982, Irish Guard Firearms offers personalized service for the discriminating buyer or collector. Before purchasing a sports, self-defense or collectible firearm, give me an opportunity to introduce you to some of the best products on the market today. This business sounds really interesting, for example maybe if someone is looking for a rare Farmingdale (or Colt, 1911, etc) you could help them find one for a reasonable fee. It seems like this service could also leverage a lot of your current customers.
Another suggestion may be to offer high end EDC products in addition to the firearms you carry such as knives (Microtech, Benchmade, Chris Reeve, William Henry), flashlights (surefire, etc). This again would allow you to leverage your current customers and current advertising as much as possible.
Anyway, just my 2 cents. I wish you and Irish Guard Firearms the best of luck with whatever you decide to do and hopefully we will get a chance to do business soon.
Best,
Ryan