Check the internet for industrial supplies rather than automotive.
RS components or Buck & Hickman have vast engineering supplies.
Measure the inside diameter plus thickness of the ‘O’ ring.(take wear into account)
The only problem you’ll get is that they may sell the kit which contains the complete range of ‘O’ rings
rather than individual sizes.
Take Duffos advice Viton is safe to about 180’ C ; as standard ‘O’ rings ( Nitrile rubber) is good to 120 'C
Just to let you know from 2nd Feb in LIDL they sell ‘O’ ring kits for £5.99 Metric & English (420 piece sets) probably Nitrile rubber ; not quite what you need perhaps but good for general maintenance.
Have a look through the illustrated parts manual and you can find the part numbers for the O rings, I got mine either from Fowlers, TLM or Gutzibits. However in the parts list some of the sizes are stated so that you can try external suppliers such as simply bearings. I would have given a couple of part numbers but I have a 8V sport and potentially the parts may be different.
Just checked my supplier for Guzzi parts;------ A J SUTTON . They have what you want £1.94 each which includes VAT & delivery. I believe you need 4 for the 2v model or 2 for the 8v model ( different piping arrangement.)
Check the exploded views on the part thumbnails (item #2) for both bikes.
On A J Sutton website you can key-in your Reg.# & it will auto direct you to the correct page if you wish.
Double check what I’ve said about 4 off or 2 off seals.