I got the PID and RTD probe from Auber Instruments, auberins.com1 x 1/16 DIN PID Temperature Controller (SSR control output) (SYL-2352) =$44.50
1 x Liquid tight RTD sensor, 2” probe, 1/4 NPT Thread (PT100-L50NPT) =$29.95
You may as well get your 40a SSR and heat sink from them as well, or find a cheaper equivalent on ebay, I already had the SSR and I made a heat sink from apple G5 parts. You really don't need much of a heatsink for this small load, mine never gets warm.
The Stainless Tees, barbs, compression fittings, etc. I got from Bargain Fittings. The RIMS tube's stubs are 3/8" OD so I used two 3/8 in OD tube x 1/2 in NPT (pipe thread) adapters and a 1/2 x 1/4 inch reducing bushing for the RTD probe.
The RIMS tube, that may be difficult to source unless freddyb still has some left. It is made by Watlow and I assume he bought them surplus or something. Here is a link to the thread that got my attention http://www.homebrewtalk.com/f51/35-rims-heater-133208/
I used plumbing strap clamps from home depot and covered them with heat shrink tube to mount it to the wood block. The shrink tube gives it better grip and should prevent from marking up the RIMS heater. Searching by the part # on the element I found this which may help you http://www.midohioresale.com/storepages/tube-heater.htm
The 3/8 OD stubs concerned me but they are short so they don't have too much affect on flow for Mash recirc but when I whirlpool the boil I disconnect the RIMS and use the march pump directly.
I would consider some kind of ventilation for the toolbox, I leave mine cracked open during the mash but I'd prefer some kind of shielded vent.