I had a similar problem recently with my SIP saw. I bought a CMT ripsaw blade (on offer) from APT, assuming that although it was 30mm bore, I would have an adapter sleeve to suit in my "bits & bobs" drawer. Well I did, but it was a 30 to 25 mm reducer, and it didn't fit ! Luckily I was able to increase the diameter to 25.4 with my baby lathe, but I do not know if you can buy off-the-shelf reducers to 1".
I am seriously considering taking off the drive from the saw and edging it down to 25mm, to save future hassle.
Colin S