A few years ago, I used Towing and Trailers, I bought 3 and took them down to a local tyre place and he fitted them for me (he'd seen to the car so thought I'd ask)
You probably know this but p6e has 2 different size tyres (it did when I bought my trailer over 20 yrs ago) the thin ones and the thick lumps for the livestock version. I know it sounds sad, but when I first saw my trailer, it was the cute wheels I liked! (So naive!! Cute wheels means expensive!! I used to own a Fiat Cinquicento, it used to tow my trailer!! Beautiful little cute, low profile tyres. ONLY manufacturer was Pirelli, due to mileage, new tyres every 6 months.)