For reflectors, I bought the Coralvue individual single reflectors. I believe the are about 2.5 " wide and they sell them in 24"&36" long lengths. They cost $10 each and shipping was free for me. IMO, they are good reflectors as far as quality.They also come with clips for mounting if you want to use them.
http://www.coralvue.com/super-lumen-output-t5-reflectors
For ballasts I have used 2 different ones. I ordered the HEP programmed start ballasts that ATI uses from Premium Aquatics. They were $25 each.
http://premiumaquatics.com/products/ati-dimmable-2439w-2-bulb-t5-ballast.html
These can be used for 24 & 39 watt bulbs.
I needed a ballast that could run a single bulb as well for my current light fixture and went with a Sola ballast from 1000 bulbs. They are local to me so I am able to pickup locally. They are also programmed start ballast but run just a little more than the HEP ballasts. The Sola ballasts can run 1 or 2 bulbs but they have a lower ballast factor. For me it's not a big deal. I don't want to run bulbs on my tank at 1.00 bf but also don't want to under drive them too much.
https://www.1000bulbs.com/product/111232/BS-E725U239R1S.html
This is what I used for the T5's. There are kits from BRS and Hello lights and several others that include wiring and end caps. Many of the kits I've seen come with instant start ballasts and there have been debates and controversy over instant start vs. programmed start ballast for the bulbs we use. I chose programmed over instant for my own use.