There's a 12% discount code for Toyo's from Camskill in the Premium members section, IIRC. Not sure if it's still active or whether it covers both R888 and R1R's but if that's now invalid, there's probably a similar one via SELOC (you'll need to be a member though).
The other option is to try and get some of the newly sized Avon trackday tyres that they've made available for the various Lotus racing series, this year. They'll have a 195/50 16 option but it may well just be another cut slick of the R888/A048 ilk.
the discount code still works on R888 , worth about £73 just on a complete set , easily worth the membership contribution