You could get return address labels in bulk at your local post office. At the post office, they are really kind with your needs and give you discount in bulk.
Websites such as Vistaprint.com can quickly and easily print bulk orders of return address labels. If you want to go to a store near where you live, any office supply store can help you order large quantities of labels. Try looking at Staples or Office Depot if you want to go to a store.
Your local printer store most likely has special address labels you can customize. They most likely offer a discount if you buy in bulk. You can also choose the color of the lettering.
Custom return address labels can be ordered from any number of specialty print shops. They can also be printed with a standard printer and labels from companies like Avery. Special label printers are also available, most notably by DYMO. The last 2 can be purchased at any office supply store
Personalised address stickers can be made on your home computer using software programs such as Microsoft Word, or Coreldraw. You can then design your very own and then print them out.
Large stationary organisations that provide equipment like this to offices across the country will have shipping labels that you can buy in bulk. Perhaps ask at the nearest Post Office.
Major office supply stores like Staples and Office Max would be able to provide you with labels in bulk, but you might also want to check out www.bulkofficesupply.com/labels.aspx for better prices.
A bulk order of business labels is not too expensive to acquire if ordered from a good retailer. These include a local print shop that will give you a big discount on mass orders.
Worldlabel offers a variety of office supplies in bulk including adhesive labels. They allow you to choose the size of the labels and the amount you want delivered.
I don't think you can put that in bulk mail but you can block them.
Labels for guns can be purchased at any store that sells guns. They could also probably be bought at any office supply store such as Staples or Office Depot.
http://www.actionenvelope.com/ is a great website for buying bulk shipping envelopes. Buying in bulk usually results in reduced prices and consistent quality.
You can find custom wedding labels at a number of stores. Your local wedding and accessories store might be able to print these up. Amazon is also a very good place to look for these labels.