I'm surprised at the difficulty you're having with Grimco, but it may be just local to the branch in Kansas City. My delivery comes from Springfield now, though when I started it was St Louis. But for us, all cut vinyl is shipped UPS free from St Louis, and arrives the next day, which it would for you too. We use primarily Avery, which they don't stock much of, but even drop shipped direct from Avery it's 2 days and still free. When I call them, pretty much all the reps there know us and I don't have to deal with any specific person. It really should be the same for you. Perhaps you should call them some time when you are not ordering something in a rush and talk to someone about the trouble you're having. Though I haven't been to their Springfield location, I have been to the Fenton location a couple of times, for an open house, to look at my printer before ordering one, and also to pick up materials I needed in a real rush. I've even arranged to have my brother in law pick up some ink at the KC location to bring down on Friday of a 4th of July weekend so we could print a big banner order. That's what has impressed me is that even though they are a big company all over the country, there are real people there and I've gotten to know them personally.
For that matter, I'm surprised you aren't happy with N. Glantz. I've used them longer than I have Grimco, since they were the primary supplier at the place I worked before I opened my own shop. I still use them as a secondary supplier, especially since their delivery truck runs on a different day of the week. Their prices are a little higher across the board, but the service is great and they sell some things Grimco doesn't.