99 civic lx cracked exhaust manifold by O2 sensor

I was able to buy a new replacement exhaust manifold online for $100 made in china but no one sells the gasket where the catalytic convertor attaches to the exhaust manifold. All neighborhood parts dealers including Honda only sell the new manifold with the new catalytic convertor already attached.
Some parts places showed the name of the gasket listed but it said they were unavailable to order. After thinking about it a while the only thing I could come up with is the manifold probably didnt crack until it had a lot of miles on it and somebody doesnt want me putting a new exhaust manifold with a high mileage catalytic convertor. Any thoughts?
I found some interesting comparisons in my neighborhood. Kragen Auto wanted $562 for a new manifold/convertor, Auto Zone wanted $401 and Pep Boys wanted $229. It keeps getting better.
All 3 stores sell the same brand by a company called Dorman.
Honda covers the emissions on the car up to 80,000 miles or 7 years. I have 100,000 miles on this car and I wonder how long it has been cracked. The parts guy couldnt tell me if the gaskets for the rest of the kit are in the box. It is a special order item. Wont be in until tomorrow.Only $20 more if I have to buy them plus tax. What a world we live in.

Really common issue. The manifold you bought will work as long as it has a place for the secondary o2 sensor. Just seal the joint between the maniofold and the converter with some quailty muffler cement. If it fails to work, remove the old manifold and send it to a weld shop to be fixed. It they say it can't be repaired, send it o a better shop. I have repaired... hundred's ... of these manifolds and by no means can I weld.