pH probe calibration solution, where and what to buy?

I know there are different types of pH calibration solutions, but which one(s) should I be looking for and where should I be buying from?

My Milwaukee pH probe came with calibration solution in a sachet, but with no re-order instructions of any kind.

I know I could always call the good folks at Milwaukee Instruments - Manufacturer of pH, EC, TDS, ORP, Dissolved Oxygen meters, monitors, controllers and testers. but I wonder, what's the /inside/ skinny on this topic? Can these solutions be had for lower prices or of better quality somewhere else?

 

By way of update, I wanted to forward on my communication with Milwaukee Instruments:

 

Thanks for your attention. I'll look at Dr Foster and Smith and That Fish Place. If anyone else has some specific suggestions to a particular retailer, I appreciate that as well.

--
Tommy Butler

 

Gotta loooooooove that instant gratification of walking out the door with what you wanted. Ahhhhhhhh.

I wish I could find a place around here in DFW, TX that had anything resembling a decent assortment of hydroponics products.