Where can i purchase parts for nilfisk sm800 sweeper ?

Castor and camber are two separate adjustments.
Castor is how far the suspension strut leans forward or backwards and adjustment is very limited.
Camber is the tilt of the wheels top to bottom measured across the car. How far apart are the wheels at the top compared to the distance at the bottom. Adjustment depends on the suspension fitted. Like castor, camber adjustment can be limited. So work out which one it is you to adjust.

tire wear is a method of diagnosing an alignment problem
abnormal wear on the insides or out sides of the tread indicates a problem with toe in/out and or camber settings
wheel wobble at speed ( 20 mph up ) indicates castor setting problems
steering wheel not self centering after turns indicates castor settings
steering wandering on the road indicates worn steering /ball joints and or alignment settings out
car running sideways ( crabbing)on the road indicates worn rear suspension parts , broken center bolts on leaf springs ,and rear alignment problems which will affect front end alignment
this is indicated by the steering wheel position off center when driving straight ahead

depending on the size --from a hardware shop or a wheels and castors shop or from a large tool shop
look in the trades section of the local phone book

contact the manufacturer of the jack for a spare castor
find a wheel and castor shop in your area as they will probably have a replacement unit or if you have to replace both castors

Tire balance first and have them shake down ft end

have a front suspension check done and replace any worn ball joints and other failed parts . Check tyres for bulges in the side walls and belt separation . Have a wheel alignment done as this problem is a Castor wobble from negative castor settings. If a 4WD vehicle with a shocky on the tie rod bar have it replaced as it is not opertaional

Most common indicators are. Wheel alignment ( not enough Castor adjustment) worn tie rod end/s Incorrect size tyres ( you have to have the rim sizes the same on both sides ) even though you noticed a difference Loose steering box / rack or worn rack mount rubbers Probably the noise under the floor as the rack is bashed up and down from the wobble. What you describe is castor wobble and some makers recommend 0 castor when in fact the setting should be 1/2 to 1 1/2 degree positive.

take it to an accredited wheel alignment shop and have some positive castor put on the suspension or stub axle setting
shimmy is from zero or negative degrees castor setting

This must be set on an alignment machine you just can't move the front wheel to what you think is correct, it must be right on. They toe in slightly on most vehicles

with an alignnment machine. If its a 4x4 and a strait axle then its not adjustable like all strait axle 4x4's Only the toe can be adjusted. Alot of trucks that are not strait axle come factory with the option to adjust those two but like my Expedition you need to purchase a part that doesnt come with the truck which usually runs about 75 bucks.