Rockford is a little far from me, but there are many stores in my area, one of which is Fish Planet located in Deerfield.
They have a great selection of fish and usually an assortment of angels. The owner is Steve and he is great at getting special order fish if you let him know what you need/are looking for. You can find them on Facebook,
https://m.facebook.com/FishPlanetStore/
There are a couple stores right over the border in WI. You probably want to call before you go. I don't go to these two as often as Fish Planet.
Aquatics Unlimited
Family owned since 1969. The Best in Tropical Fish. Over 12,000 sq. ft. of livestock and products. Shop tropical fish and aquarium products online.
aquaticsunlimited.com
The Fish Factory
thefishfactoryonline.com
There is also these stores in IL
Animal Island in Midlothian
http://www.animalislandpets.com/
Birds and Beasts in Crystal Lake
pet shop, retail
www.birdsandbeastspetshop.com
Trop Aquatics in Lombard
Tropi Quatics, Lombard IL, has been in business for over 40 years and have the best connections to get rare and hard to find freshwater and saltwater fish. We have almost 10,000 gallons of fresh and salt water. We receive weekly livestock shipments.
www.tropiquaticpetcenter.com
There is also a larger fish store that isn't a Mom-Pop store. It's located in Schaumburg or Bolingbrook and called Aquarium Adventures.
aqach.com
I was going to recommend Old Orchard Aquarium in Skokie but was sadly surprised to see they closed. I knew they were selling, but I guess it fell through. It was a great shop with a ton of fresh and saltwater fish, plants and supplies at good prices.
Lol, I have kept fish for over 20 years and try to visit the local and not so local stores when I can. Hope this helps somewhat, I realize many of these are a considerable drive from Rockford. Good luck.