Yes, definitely add Noonans. Davissons in the US do a regular list and auctions. There are different specialisms amongst auctioneers, some you may find better for what you want to collect than others. A quick search of coinarchives.com, numisbids.com and mcsearch.com (acsearch for ancients/mediaeval) might help there.
Dealers similarly. Mike Vosper for ancients, Lloyd Bennet has a good selection including more modern pieces, AMR coins for good higher end. If you look at their sold archive you'll see if what you want features regularly enough. Many dealers will accept a 'wants' list, which might be worth considering?