Not sure how small you mean by small, but there are some in the 70 to 100 lb range that will run off 120 volt ac or 240 volt ac. If you are looking at older machines, Bauer made some small ones called Varius and Purus which pump between 2 and 3 CFM which is about as small as practical. They are discontinued, but many of the parts are still available. Rix makes 3 and 6 CFM oil-less compressors which are portable. The newer bauers (Junior, Oceanus, Capitano) are degrees of portable, but each step up requires more power and is heavier. I don't know a lot about the coltri, but I think its been around a long time and it seems pretty portable.
If you provide a few more details of what you are thinking I'm sure the experts on here could provide more guidance. How many tanks are you filling, how much weight or size can you handle, what is your power situation (i.e. 120 VAC 15 amp house plug, 220 VAC 30 Amp dryer plug)?