Darren, For our OTK karts, we used EBC FA540S brake pads. I’d get them off of ebay from a Kart shop in the UK for $15-$20 a set; yes, a SET.
My Son raced Rotax Masters and won many National events with these from North Carolina to Sonoma.
He won’t use anything else.
Once a day I’d have to hit them with a file as they have a high metal content.
We used the Green “soft” pads even in the hottest temps and never had an issue.