substituting chicken stock for turkey stock?
I use boxed Swanson's plus a bit of water as the base for my turkey broth - NOT stock, really, since I cook the giblets and neck to be eaten, not to extract all the goodness. So the turkey parts are really just enhancing the flavor, not giving up their all to it.
I will probably go through a good half-gallon of Swanson's before the day is done.
You can make your own turkey stock by simmering the neck (and some people like the giblets) in water with some bay leave and maybe some parsley, salt, and pepper. Then use that to deglaze the roasting pan from under your bird (scraping up the crunchy bits), then strain that and let the fat rise to the top, spoon or pour off the fat, and use the resulting, very flavourful stock. Or...
Buy turkey stock at the store (I've seen it). I buy turkey base and make my own stock sometimes.
However, to answer your more direct question, yes, you can use chicken stock instead, if you like. You could use apple cider instead, any water-based liquid will be useful for making the stock. It just won't have as strong a turkey taste if you use chicken stock is all. :) That matters to some folks, not to others.
This time of year you can find turkey stock in the grocery store in shelf-stable cartons. I picked up some Kitchen Basics, but I know I saw at least one other brand, maybe Swanson or College Inn. I think Better Than Bouillon makes a turkey base. I plan to taste the Kitchen Basics soon to see how salty it is. If it's too salty, I'll get a couple of wings or thighs and make my own stock as Niki suggests.
Sure, you can, but it's not very hard to make some turkey stock. If you're roasting a turkey, just use the neck and giblets to make stock. Put them in water in a saucepan, add an onion and a piece of celery, cover, a pinch of salt (no more than that, because the liquid will reduce but the salt won't) turn it on low, and let it cook for a couple hours. Viola - turkey stock! If you're not roasting a turkey, buy a couple of turkey wings, roast them in the oven first (this will add depth and color to your stock) then proceed as above.