I bought it at a local store. You can use any thermal pad, the main thing to match the thickness. Also, I advise you to first try to install something 0.5 mm thick to make sure that the distance between the copper tube and the housing is 0.5 mm or slightly less.
Pro Legend PL4200
https://technopoint.ru/product/5840ebd20bb53330/termoprokladka-pro-legend-pl4200-sale/