Call every butcher in the area--especially those you know or think might cure their own sausages--and see if any have and will sell you sodium nitrite. If not, try the pharmacies, especially the older Mom-and-Pop ones--but be sure to specify
food grade sodium nitrite.
If you can find it (you don't need much) it
cannot be subbed 1:1 with TQ--you have to make a mix. But it's very simple to do.
Barring that, you can order on line. Though you can get TQ, I'd recommend getting curing salt and making your own curing mix. It's much cheaper and more recipes are written for a self-made mix than for TQ, e.g., recipes for bacon, cured sausages, etc.
DQ Curing salt is available
here. (Remember that straight nitrite, or products that contain nitrite (like DQ or TenderQuick) should not be mistaken for regular table salt (DQ and similar products are dyed pink as a reminder). Though safe in small quantities, they should only be used in the exact amounts specified in recipes and should be kept out of the reach of children.)
If you order on line and decide to get DQ instead, grab some dextrose as well (on
this page). It works a bit better than table sugar (sucrose) in cure recipes as it is finer and less sweet.