John
Unsure where they would be available other than the dealer. Not saying they aren't available elsewhere, just saying I don't know.
You need the new style filter and 3 plastic preshaped lines, unsure of the part numbers of all that. It hasn't struck me that they were terribly expensive, more labor intensive than anything else.
There IS an outside chance that you may be able to get it done free, however that may be extended only to the original owner. You can certainly ask at a dealer to see how nice they are.
On a 99 with an unknown service history, I'd recommend a B service (which includes the dust filter), a coolant and brake fluid flush, air filter and fuel filter (which are both due at 60,000) and spark plugs (which are due at 100,000mi OR 4 years)(overdue probably based on time).
Remember the truck still has roadside assistance, the phone number is on the inside of the sun visor mirror cover on the drivers side, it doesn't expire. Good for a jump start, flat tire or out of gas, anyways. Better than any other car has at this mileage.
Which reminds me to tell you to make sure they check the battery on the B service if it appears to be original.

Gilly