Welcome to the Forum.
They have Timothy Grass at Murdoch’s (like a ranching and farm store), which I go to. I was originally going to get the Timothy Grass for my guinea pigs, but the lady working there informed me not to. Timothy Hay and Timothy Grass are the same plant, however, Timothy Hay is fully dried. Timothy Grass is also dried, but not to the same extent. Since I “only” have three guinea pigs, the grass would be more likely to mold or go bad by the time my girls would be able to finish the entire bale.
If you have a lot of guinea pigs then I recommend getting it since the smaller boxes can be costly.