I am installing a new master cylinder on my 82CE (had new "O"ring calipers and SS lines installed 18 months ago).  The GM SHOP Manual shows two round gaskets that mount between the MC and the Power Brake Unit.  The gasket closest to the MC looks like a thick flat sided ring and the gasket clostest to the PBU is thin flat sided with 3 nobs on the inside and evenly spaced. 

I had the same thing happen to me at the Napa Store here. I ask if he had the gasket and he said they never had one. I argued with him for a while and his mgr said he had never seen one either. So I put it together without it and as far as I know it works OK, but I have only put maybe 15 miles on the car since I'm in the middle of rebuilding it.

The more time you take bench bleeding the MC, the happier you will be when you mount it.  It took like what seemed forever to bench bleed mine, but it meant almost no time to pull thru with a pressure pump at the wheels after install.

There might be a thin. paper-type gasket that goes between the MC and the booster, on the flange area(where the studs/nuts go). Not really needed, tho.
The only other thing that might be considered a "gasket", just by looking at the service manual pics, is the rubber grommet, on the booster itself, that seals the pushrod to the booster assy. Unless it falls out when you remove the MC, or is really "squishy"(technical term there, folks!) or swelled up, it will be fine. You'll have a hard time finding that particular grommet anywhere, except a brake specialty shop/supplier, as far as I know.
If your brakes are not hard to push when driving, the seal/grommet is prolly otay.

btw..hope yer feelin better!