you can clean them yourself in an ultrasonic cleaner using a seafoam blend with kerosene and then flow rate them as well. I have a test setup with a CIS pump and a djet regulator set at 32 psi and fire them into calibrated test tubes. Its not for the faint of heart and for the $25 each from rock auto I would probably advise that route if you are not pretty handy with mechanical stuff.
the end cap is replacable - its called a pintle cap and I buy them by the bag (100) for a dollar each from dr injector or somewhere similar. there is a long nylon mesh basket in the top of the injector which should also be pulled and cleaned
I am currently converting one of my megasquirted engines from the bosh 036 injectors to the 290ml JECS injectors off a couple of nissan zx300's. remember with the nissan injectors that the number on the body is a date and production facility stamp and does not relate directly to flow rate. flow is determined by the colour of the body not the number.
there are a couple of pics below of how I do it but I use mt stimulator to fire the injectors and you are playing with gasoline under pressure and the possibility of electric sparks!
cheers
Barri