I want to make my own rub and am looking for such items as dried apple powder/flakes and dried lemon. Is there a favorite place to get such rub ingredients without costing an arm and leg?

To answer your question, No.

You might be surprised how easy to do at home.  Slice both the apples and lemon, rack and put in oven.  Most oven will go down to 170°.  Let them dehydrate till hard.  Run through Ninja, Bullet, food processor or coffee grinder.  The best part is you cant over dry them, so it just a matter of finding the sweet spot for moisture content to get to the powder state you want.

https://www.americanspice.com/

Used to shop here all the time when it was based in Fort Wayne. I haven't bought much from them since they moved to Michigan, but I assume it's still all good stuff.

Lots of specialty powders, etc., however I just glanced and did not see apple. Could have missed it though.

 
 One of our bulk food stores here in Canada, Bulk Barn has a lot of what you are asking about.

I frequent an Amish market about an hour from here.  They have a lot of supplies in bulk, very reasonable in price.

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https://www.americanspice.com/

Used to shop here all the time when it was based in Fort Wayne. I haven't bought much from them since they moved to Michigan, but I assume it's still all good stuff.

Lots of specialty powders, etc., however I just glanced and did not see apple. Could have missed it though.

I've bought from them several times too