I am looking to floor 3 condo units, they have a long hallway with a living room, kitchen an bedroom to one side of the hallay.

logical method is to start in hall and install floor toward these three rooms..

the issue is there is one bedroom behind where i am starting. with full 3/4" i would install a spline. however for the engineered that i am using the vendor doesnt have a spline.

is there a place i can buy spline online? could i shave a larger spline down? is there a another method the experts use?

Just make it on the table saw. I usually use the top portion of the tongue and groove side of the hardwood I am using. May take a little tweaking to get it to fit just right but its easy to make.

I bought a piece of 3/8 or so oak board and used my table saw to cut the right width for the groove and then glued it into the piece I was using as a spline. I then cut lengthwise on the splined board so that the correct amount was hanging out to fit into the receiver (female) piece. Hardest part was getting the corect width so that when I slipped it in the grove it wasn't too tight or loose. Made several of these to go across the length of the room. Worked like a charm.

Test fit your boards on the bench and you will be fine. I think a little loose would be better then too tight. You can always use some glue to fill any void if it's slightly loose.

Good luck.