Hey Twister!
Mantech (in Joburg, anyway) don't have a minimum order quantity, and you can buy over the counter but the queues are generally long- it's easier to buy online/phone through an order and then go in to collect. The piezo disc buzzer they sell works great for a CBG pickup- I used one in
the 2 string bass I built. You really need a preamp/buffer if you;re using piezos though, so a cheap strat pup is probably the easiest option.