Buy orange tulip seeds from Loid and plant them. Harvest the orange tulips and x-pollinate with a blue tulip at a friends's garden. You'll get orange and white tulip seeds. Plant the orange and white tulip seeds you just obtained from the x-pollination. Harvest the second-gen orange and white tulips and x-pollinate them with a blue tulip at a friends' garden. Approximately half the resulting seeds will be for blue tulips. You can plant one and keep it so in future, you won't need to find a friends' garden to do more x-pollination.
I didn't find this out myself but read it in a guide on Reddit. I can confirm that it works, I've so far managed to breed 80+ blue tulip seeds and I'm still working on getting more.