If the glass is flat it is not a problem to get new glass. You just have to find a glass shop (not an auto glass installer). If it is curved glass your going to be in trouble.
I have had glass cut for a few pieces of equipment by different glass companies. I will make a template out of 1/4" underlayment or take all the broken pieces in taped together. They will then cut it to your specs. If there are holes in it make sure to bring the attaching hardware for a fit check. Remember auto glass installing folks are the wrong crowed to talk to, they know how to order and install glass. Folks who do Picture frames would be good to talk to as they do some odd frames some times. The lumber yard might know of a glass cutter also. The glass cutter does not care if it is for a house, a coffee table, a piece of art, or a tractor, they will need to know to use safety glass though.
Google is your friend. here are some ideas based around Medford, WI.
We offer auto glass windshield replacement, windshield chip repair, and more in Central Wisconsin.
autoglasswi.com
It might not hurt to call the local window manufactures as well.
Designing and manufacturing the highest quality windows and doors. Continuous innovation. Bet in Class Warranties. Design flexibility. Energy efficiency without sacrifice. Family-owned and operated.
weathershield.com
www.bigbluewindow.com/
I know I have had to call lots of folks and get turned down lots of times before I found the right glass shops. It takes time but it is worth it and is much cheaper than buying a new cab.