Just go to eBay or Amazon and search for "grocery pannier". Some may not fit exactly perfect...or you could wait until radbikes get new stock of their "made to fit" panniers (you might inquire when they expect some from customer service). I ended up making modifications to a horse saddlebag set to fit my radmini.
For a a huge selection of quality bags in a wide variety of sizes,, and my primary source for bike stuff, https://en.hollandbikeshop.com/bicycle-bags/double-panniers/ Make sure to select USD, and United States as destination to get price without the 19% VAT tax. Prices are so much lower for many bike items in Europe that it will often more than make up for the cost of shipping.
De Poort and Willex are particularly high quality bags from Holland.
I have this. New to me and I have not rode with it yet but it seems to fit. I shop for one, so not much need for bigger bags. I bring the bike in and use it as the cart. So far no one has bothered me about it. I turn off all my lights though so I don't blind people. I am getting my bike back from the RadShop today and will report back with a review. https://www.amazon.com/Docooler-Mul...e=UTF8&qid=1488054588&sr=1-8&keywords=pannier