Sid, my understanding is that "Manila" is commonly used as root stock in California, so you can either buy seedlings already started or just buy some locally grown Manila fruit, and plant the seeds. Florida root stock ( generally Turpentine ) does very poorly here in the DR. and have read it does not do well there in California, couple years ago or so, I planted a Manila seed, and I have never seen any other local variety grow so fast. I intend to use that tree as a source of fruit for seeds, the fruit is not bad also.
It's so much easier to just go out and buy/order a Alphonso tree, but I understand many want to start from scratch and do it themselves. it is exciting to start your own seedling and graft onto it. you still need access to Alphonso scions though.