Not sure of the question...is it "What's the best place to buy injectors?" or "Where can I buy the best injectors?"
If the latter question is right, that answser is easy:
RC Engineering. If you want good injectors, use a few of the sources listed in various places on this forum, but keep in mind, a some of that stuff is just used injectors which have been cleaned ultrasonically. They are not new and are not even "remanufactured" in the sense that legitimate business use that term because stock LT5 injectors cannot be remanufactured nor can most other injectors used in an LT5.
If you want the best injectors for 1G LT5s, go to RC Engineering. More than two decades ago, the late Jim Van Dorn and I worked with RC Engineering to develop a set of high-end replacement LT5 injectors which would support at least 500-525-hp yet offer good driveability in all situations. RC Engineering continues to sell them today. They are a derivation of the Lucas rotating-disc injector design which was a far better choice that either the Bosch pintle (ie: Ford) injectors or the ACD ball and socket design.
If you are interested in the best injectors you can get for an original LT5, contact RC Engineering and ask for Wayne San Miguel who understands the 1G LT5 injector situation.
RC injectors are not the least expensive but they are an outstanding product. I installed a set in Barney's 500-hp Automasters "Street Skinner" engine in 1996 and they were still in the car when I sold it 20 years later. When I owned it, they were in-and-out a couple of times during plenum-pulls. I sent them to RC for cleaning and retesting. Each time they came back with a flow spread of 1.5% and "execellent" patterns.
Since I sold Barney, I continue to use RC Engineering injectors. I have a set on my '04 Z06 which have been there for about 13 years trouble-free. I just had RC clean the OE injectors out of my '12 ZO6. They came back with a flow spread of 0.9% and exccellent flow patterns.