Inracing in Nottingham does a repair kit for the Bristol fuel pump (along with a wonderful - or frightening, depending on your finances - range of other engine parts) at
https://www.inracing.co.uk/RACING_CA..._Engine_Parts/.
Mine came with a variety of gaskets and sealing rings which included ones to fit my 100 series engine OK.
The kit is fairly cheap, but the postage is expensive.
Hugh