I've purchased from buyrocketmotors.com and wildmanrocketry.com the past couple of years, and was happy with the pricing, products, packing, and service.
Looks like Wildman carries the motors you're looking for. I usually buy my F50 and G40-sized SU AP motors from him by mail in quantities large enough to make the per order Hazmat cost "reasonable." But it also looks like his prices have gone up significantly since the last time I ordered (in 2015). And I recall last time my order from Wildman took quite awhile to arrive. (Prob because I ordered during the weeks of LDRS and TARC.) I once tried to buy motors from the Wildman at a launch but was disappointed that he didn't have the ones I needed in stock, so I usually plan ahead, bite the Hazmat fee bullet, ahead and order thru the mail.
I recall Sirius Rocketry was also selling Aerotech SU motors last time I was shopping. But they were pricy as well.
Now that I've taken a look, ncphobbies.com prices do look pretty good.