I just purchased a 182J with an air glass nose fork with 8 inch tires on the mains and a 6 on the front. With a 50 pound sandbag in the baggage compartment and two adults in the front, it takes a lot of effort to get it to land on the main wheels without also touching down on the nose wheel. Is there a way to adjust the nose wheel scissors to limit the downward travel of the nose gear in flight, to allow an easier touchdown on the mains only?

By 8" tires I'm assuming you mean 8.00s and 6.00 on the nose? You should be bale to land mains first no problem with that setup. If you push the tail to the ground when sitting on the ground how far off that ground is the nosewheel? Should be a few inches for sure. It sounds to me like you need to work on landing with more of a tail low attitude. Either carry more power so you have a bit more elevator control, or Just put a bit more muscle into keeping the nose up.
You cant shorten the scissor links, and you need them to extend all the way to keep the nose wheel centered.
Now if you push the tail to the ground and the nosewheel is basically still on the ground, there is a good chance that the nose fork wasn't installed correctly. The strut tube is supposed to be cut off on most installs.
But I would start with checking how much nosewheel clearance there is with your tail on the ground. Most other Js I've worked on have a fair bit and no problem landing mains first.

That is exactly how my 182 wheel set up was. If I didn’t roll out ALL of the elevator trim on short final just before touchdown I struggled with heavy nose.

Mine was a P model. The wing may have helped for slower landings, more nose up.

Do you have an aftermarket wing cuff?

Here is a pic of stance for comparison.

I echo the feedback about technique. I spent a lot of time flying a small tail 182 that needed very good technique to land properly. Don’t drag it in, you need enough energy to rotate and carrying a little bit of power helps a ton because of the extra airflow over the elevator.

I've even seen some suggest rolling the trim full nose down so the trim tab gives extra elevator authority, but I couldn't get used to that technique.

First, you don't mention what flap setting you're using. As A1 Skinner noted, the strut is supposed to be cut off during the install, but those 182s with small tail feathers just don't have enough horizontal tail surface to land well, in my opinion.

But, try full flaps if you haven't been already, and as others noted, full back elevator in the flare, and a touch of power at just the right time will get it done properly.

Alternatively, put a set of 8.50 x 6.00 tires on the mains. That will also help immensely, and look cool to boot.

Like A1Skinner alluded to, was the nosefork installed properly? Check this pictorial from Airglas: http://www.airglas.com/Portals/6/NWDS_StcFiles/3/Nose%20Fork%20Install%20Pictorial%202011.pdf

8.00x6 on the mains and 6.00x6 on the nose shouldn’t be too hard to land.

Have you tried less flaps? Full flaps have a large forward pitching moment. In my 205, the difference between 30 degrees and 40 degrees is significant. I usually land with less than full flaps when I’m light/forward CG.