You don't really need a specific "brand" you just need to find a tile with the characteristics you are looking for.
If you are wanting to do "coasters" you need to find coaster sized tiles that are somewhat smooth, non-glossy and have a very limited protective coating. Almost all of them come from the factory with some type of coating for added strenghth but some have more than others. If they have an over emphasised texture (like deep line, gouges, or grooves) your stamped image will not penetrate into those spots which leaved your stamped image erratic. If there is too much protective coating on them they will not absorb the condensation from the cups that you place on them. I found the best place to get my tiles is at Lowe's and they are about $0.50 per tile, the Menards here does not carry anything like that.
You can stamp on the glossy tiles as well, however, these tile will not be suitable for "coasters" because they have no absorbing features. You also have to seal them with an acrylic sealers.
Hopefully this help you out somewhat.