They are just a standard sized bearing.....can't remember the exact sizes now, but they are nothing special.
The main issue with the PT hubs is they come fitted with really rubbish bearings! Cheap and nasty old things that corrode as soon as you get a sniff of water in the air. The standard bearings are junk.
This combined with a pretty average design means they will wear out very quick. Send it back to Saris and you'll get another set of junk bearings fitted that'll need replacing in roughly the same time period in the same conditions.
I used to do lots of PT builds for people and became quite experienced with the ins and outs of them.
If you're in the UK http://simplybearings.co.uk/shop/
These guys have everything you need.
If you're in the US there are loads of bearing shops online.
My advice would be to go for a high quality bearing that is water resistant (you can pick up what is effectively a stainless bearing set for not much money, just check the specs and look for blue seals) Fit them carefully and you'll be good for a couple of years at least.
The PT hub is a doddle to work on, very simple design, no problems.
I think I have the sizes and bearing codes around somewhere if you need them, but best solution is to remove and measure.