You might be able to get these off Mike Feeney of MJP.
It also acts as an insulator to keep the pump from becoming a heatsink.
Cheapest I know of ...
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/323771414228
YOu need a gasket either side too. Speak to the seller to combine postage ...
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/333158254405