[clug] spare RTL SDR dongles?

[Bob Edwards]

Hi all,

I am likely going to run an SDR exercise with a bunch of high-school
students in a week and a half, but approval has been slow coming so
I am now in a situation where the event may run but I don't have
sufficient dongles - I need about 20. I am about to order some but
I am seeking advice:
  a) can anyone recommend a fast, cheap and reliable supplier? (or pick 
any two)
  b) does anyone have a spare RTL SDR dongle or three sitting around
that I could either buy off you or borrow for a day?

Thanks for any assistance in advance.

Bob Edwards.