Staples has a large variety. Some Wal-Marts, but not all, also have a large variety.
You might check other office supply stores as well.
No one asked for my opinion, but here goes. The rollerball refills come in many different brands, from the approx. $5.00 each for the Mont Blanc to the cheaper versions. For rollerballs, the best and longest lasting I have found is the Pilot G2, which comes in a package of two for less than $2.00. The Parker brand is best for the Parker type pens, and I use the Cross brand refill in the Cross type pens.
The Parker brand and the Cross brand are more expensive than the ones you can order, or the ones that come with the pen kits, but the writing quality is so much better.
If I am selling a pen in the $30.00 range or higher, I feel the customer is entitled to the best writing insert available, and not one that barely writes, and if it does write, only lasts two or three weeks, as the Mont Blanc rollerball did.
I have seen the Parker style, made by Cross on the shelves, but I haven't tried one of those.
Bonefish
