My preference is to vent the fireplace to the outside. These gel and ventless fireplaces are nice if you use them every now and then, in my opinion (IMO). IMO, they dry out the house and can be an 'irritant' to people whose lungs are sensitive or to those with allergies or the like. If, for example, you have a sun room that you want to take the chill out of, I'd say go for it. But if your intention is to heat the house (sort of) or to heat many rooms w/it, I'd recommend a unit that vents to the outside. Again, it's my opinion.
As to your question of where to look at fireplaces that use gel (et al.), look in the YELLOW PAGES (under FIREPLACES) and start calling. The WEB has Search Engines for Yellow Pages too. In the meantime, you can look at some of the 'hits' at My Favorite WEB Search Engine for these types of fireplaces (again et al.), and so on. Some of the 'hits' may not apply but I'll leave the 'sifting' up to you.
If you have more questions after reading about them, post up. For now, my best to ya and hope this helps.