I've heard others mention that Allens Performance stock the re-furb kits for the vacuum pumps.
https://www.allensperformance.co.uk/.
Their virus restriction pop up notice is unnecessarily racist though!
Some owners resign to cranking the motor until enough fuel gets to the carbs, but the battery needs to be in good nick to cope with that. Taking the plugs out will give it an easier time and you will probably smell the fuel when it comes out of the plug 'oles.
Don't keep cranking until the battery fades, and probably a good idea to re-charge it after that exercise.