JimboZA:
A clue about your location would help, even in this age of online shopping.
When you say scaffolding, I'm guessing you don't mean as used in civil engineering construction, so I don't know what you do mean.
Sure of course. Im in the US, west coast.
By Scaffolding I meant more like, framing or pieces I can use to mount components too (like completed boards etc.) or slide railings like those found in some 3D printers. I'm also looking for things like bearings as well.
CrossRoads:
This place seems to have tons of stuff like that. http://www.servocity.com/
Sparkfun I think is also getting into this area. http://www.servocity.com/
altho maybe not quite as organized yet.
Depending on where you are at on the west coast, be sure to check out surplus suppliers and "industrial junk yards" as well.
Especially if you are in or near the San Jose area of California! The Los Angeles area also has more than a few. Just be sure to wear old clothes and expect to get a bit grubby (for certain places, it is advisable to bring gloves and boots - especially if it has an outdoor yard).
Realize that retail outlets as have been offered - while great places to get exactly what you need - will in the end cost more than a bit of cash. For instance, Servo City has a great robotics construction system - but it doesn't come cheap once you go beyond simple constructions.
In general, if you need to keep within a budget - using raw materials (plastics and metals) - as well as surplus parts, then machining and fitting everything together yourself with whatever tools you have on hand will ultimately be a lower cost method (although the time/money factoring can come into play here as well - as you'll be doing a lot more work to get things working properly than had you used pre-machined and standardized components).