Hi there, welcome to the forum.
The XBR is really easy to live with and has few real problems.
The big maintainence item is regular oil changes - forget what the manual says, you need to change the oil every 1000-1500 miles as the top end is prone to wear if your run old dirty oil - 1.4 lires of 10w 40 or 15w 40 at a change or 1.6L with a filter change - change the filter every other oil change.
Oil level check - warm the engine up with the bike on the centre stand. Once it's warm let it tick over for 3 minutes then switch off and dip the oil tank without screwing the dipstick in.
valve clearances are inlet 0.10mm and exhaust 0.12mm - at the same time check the free play on the decompressor lever on the head - it should be 1-3mm - if this is set wrongly it will be a bugger to kickstart! Valves don't need doing very often.
Otherwise it's pretty reliable. Front brake caliper can tend to stick and will need cleaning up occasionally. You can get stainless brake pistons and slider pins which help. If you can feel the back brake pulsing through the pedal then the drum lining may have gone oval - this is a problem as the liner is pressed in and very thin so you can't skim it round. Get a chain oiler as big single can wear chains quickly although the XBR is too bad.
There are downloads for the manual online . For Spares try Wemoto.co.uk or David Silver Spares. Most spares are still available though some bits are getting scarce.
If you need any specific part of the manual let me know and I can email it to you.
They are a nice bike, you'll enjoy it.
