Second crop is basically the second time they cut a field, so you unless if you live in a place that is able to cut hay all year around you will get what ever is stored from this previous harvesting season. However, depending on how large of a farm that your supplier lives on it would depend on if they are going to sell what they have saved up. For example, we do not sell our square bales to others, if they want hay, they're buying it in large round bale quantities. Your going to have to talk to the farmer you plan on getting hay from.
I've never heard of it being too rich, correct me if I'm wrong, but since that hay from a farmer hasn't been sitting in a bag for however long, it is generally fresher and has more of the nutrients to it. I would just make sure that it hasn't been stored for over 6 months. Also, if you get a square bale, break it up outside, we've had snakes and mice get baled up with the hay, it scares the day lights out of ya, but they're dead.
I would also make sure that you know what kind of cut your chinchillas like, first crop has a lot of stems and is very coarse, where if you get into the 2nd, 3rd, 4th, etc. crops they have more leaves and flowers in them.
I wouldn't buy a round bale if I were you, it'll rot before you get through all of it, I'd ask for possibly a square bale or half of a square bale. That is a lot of hay, and you don't want to waste your money on the chance of it becoming rotten or other critters getting in to it.
Just remember that if your getting alfalfa hay as well not to feed it as often as your timothy hay, because chinchilla pellets are alfalfa based and you want to divide up the different nutrients that are in each types of hay.