Use the Internet to search for multitrack tape machines; do some research to find out what models are available, and what the differences between the different models are. Decide on what you want to use your multitrack tape for, how large must it be, and any other specifications that will suit your needs.
Search the Internet for the multitrack tape machine model you've decide you want, after your research. Use a trustworthy site such as eBay to try to find the model you want.
Create an account with the site on which you have found the model you want. Order and purchase your tape machine on this site; your machine will be delivered to your address.
Use the Internet to research what type of multitrack tape machines are available, and what models seem suitable for you, before heading to a music store.
Go to your local audio store and speak to an expert. Tell him what you plan to use it for and let him recommend models to you.
Purchase your chosen model from your local audio store; the advantage to this is that you will usually get a guarantee whereby you can get your machine fixed by the store at any point within an agreed-upon timeframe.
Find out where your local secondhand stores are, particularly electronics stores such as Cash Converters.
Phone the secondhand store and ask whether it has any multitrack tape machines. Although you are less likely to find the exact model you want, you may find a great bargain at a secondhand store, which will be worth the compromise.
Go straight to your local second-hand stores and physically search for a multitrack tape machine; you may be less likely to find what you're after, but if you do it can be extremely rewarding.