Castin Craft and Silmar are the ones I remember now. Prices are pretty variable, so shop around. You should be able to get clear polyester casting resin for $30 - $40 a gallon. Typically the catalyst is included at no extra charge. Look around in art/craft stores, model shops, fiberglass resin dealers (if you are luck enough to live in an area where boating is popular) and the internet.
If you do a little research on the web (and you should) be aware that there are different types of clear casting resins (polyester, polyurethane, epoxy, other?). They all have different properties and requirements, but frequently people don't identify the actual resin type they are working with in their comments. My comments below are all related to my experience with polyester resin.
I didn't find vacuum necessary for what I was doing. If you decide you need it, your mold should be at least five times the size (height wise of course) of the pour volume. You only have a limited time to apply the vacuum, but if you pull too much too fast you'll learn all about exploding foam. That foam and the internals of a vacuum pump don't mix well. You also need to limit the vacuum so you don't vaporize some of the components of the resin (essentially low temp boiling).
I have found application of pressure useful in some cases. 20-30psi.
Pressure and vacuum should only be applied using appropriate equipment. You can kill / maim yourself / others if your vacuum / pressure vessel fails.
Polyester resins are different than epoxy resins. Even if you are an expert on epoxy resins, do some tests with the polyester resins first. Polyester resins use a catalyst. Epoxy resins use a hardener. The ratio of catalyst to resin is not as critical in polyester resins as the ratio of hardener to resin is in epoxy resins. This is good news and bad news.
The catalyst creates heat which is what cures polyester resins. More catalyst = more heat. Larger volumes (thicker) also means more heat. Molds that act as insulators mean more heat. Too much heat will cause undesirable results. You need to adjust the amount of catalyst to compensate for volume and mold properties.
As with any resins, protect yourself from fumes and skin contact.
Good luck and be careful.
Ed