Having just bought a load of RT moquette, we have been trying to source suitable seat foam in the UK for commercial use, as it is very expensive in France. We have found a company in Kent near Maidstone, they are off junction 4 of the M20 toward Tonbridge who can supply the wedges for the cushions and seat backs cut to shape plus the reconstituted foam needed for the seat ends to maintain the square ends. The company is Martin Upholstery Supplies, they are very helpful. Look here.
http://www.martinsupholstery.co.uk/main.html
The price for an RM is different to that of an RT but would be in the region of £260 - £280 plus VAT, but this is fire retardant and will last many years.

For further details of the grade we bought which is as supplied to Arriva feel free to E-mail me.

My bus number (if any): RTL 960 RML 2667, an RMC and now RM 1585 as well