Make them if you're in a hurry, but I don't think they'll be prohibitively expensive for just a few gaskets.
It's also possible they aren't available, but I'm betting they are. Seems like that for most of the old equipment, the gasket sets are no longer available, but individual gaskets are. Just costs more that way.
The precleaner jar might hurt a bit from CAT. Someone had some on here for sale a while back.
I got engine gaskets within the last year for a D2 5U engine, nearly ev ery gasket in the engine. All were readily available from Cat and not all that expensive. Also, consider that Cat uses a better material than I can buy at regular auto parts stores, they are cut very clean and they fit.
There was one that had to be ordered. It's about the size of a playing card and they insist on UPS shipment so there was about $7.00 freight on a gasket that cost about a buck, so you might have to consider that if they don't have all items in stock.
Something to remember when ordering parts from Cat is that if they don't have what you need at the store, they're part of a network and get stuff from other dealers. What I do is order the parts and tell them that I'm not in that much of a hurry so when they order stuff from other stores to just piggyback my order. Usually saves money that way vs having a special shipment with just my stuff.
The precleaner jar for my D47U would have run around $25 but I found a large mouth pint Mason jar fit nicely, just had to wrap a turn of parachute cord below the ring to make it fit snugly.