A quick Google search turned up "Orlando Grocery Express," which apparently delivers to Universal. I'm sure there are others.
I think the reason it doesn't often come up is that unlike WDW, where many guests are arriving via DME and don't have access to a vehicle (or would have to hire one just to go get groceries), everybody has to get to Universal (directly, or from the airport) with their own car, or one they've hired, so most folks who want groceries just add a grocery stop to their itinerary en route to their hotel. At places like Publix and Walmart, you can even pre-order what you want and have it waiting for you to pick up, so you don't have to pull items from the shelves yourself yourself if you don't want to. (FWIW, we take a hired towncar to Universal -- at a cost of about $60 each way -- and all the reputable towncar/limo companies seem to include a free grocery stop if you ask for it ahead of time. With a Walmart pre-order waiting for us, the stop takes all of 5 minutes and we're on our way -- although we're only picking up half a dozen items or so, so even if we split up and searched the store to get everything, we'd be in and out in 10 minutes).
