I need to find a slip yoke

I assume that means the entire front drive shaft is missing. Your best bet is to visit a pull-your-own-parts salvage yard. If you are anywhere between Ohio and southern Georgia, do a search for "Pull-A-Part" and see if there is a yard near you. I have been to sixteen of them. All are very clean and well-organized. Parts are inexpensive, and customers and employees are very friendly and helpful. You pay your buck, take your own tools, and you can spend all day there. They have added new yards to the southwest too. You can do an inventory search to see which yards have trucks like yours, but that will not tell you which parts have been removed, or the colors and options on a vehicle. There are a lot of other similar yards all over the country, but none are as clean as the Pull-A-Part yards.

I think I get what you mean. The yoke is still attached to the transfer case and the differential, but the drive shaft is a two-piece assembly and you are missing one of the pieces with its universal joint. Regardless if that is right or it is some other piece you are missing, this is still a salvage yard item. I would be very surprised to find there are different lengths. When a truck model is available in two-door, four-door, and extended cab models, the dimensions related to the engine, radiator, transfer case, and transmission do not change. It is the rear drive shaft that will be longer or shorter. The only potential variable I can think of is if there were optional front axle sizes, and the larger one had the yoke closer to the transfer case.

As an alternative, every larger city has at least one machine shop that specializes in building and repairing drive shafts. If in doubt, as at any large truck repair shop or truck stop. The people there are likely to have exactly what you need sitting in a corner, or they can tell you what size you need.