To be honest I've never seen a central vacuum unit in any big box hardware store and I've spent rather a lot of time wandering the aisles of hardware stores in recent years.
Then just go to a central vac specialty shop. I guarantee you that these parts exist and are available at retail nearby if you live in a city.
You can find these things online as well. Google 'em.
To be clear, this is thin wall, 2" OD, clear PVC pipe which has a slight blueish tint to it. It is NOT schedule 40 and it not compatible with Sched 40 plumbing fittings. It is designed to suck air, not carry water. 90 degree tight elbows are about $1.25 a piece. A multiplicity of other parts exist to assist you in building your manifolds.