A relocation could be performed in the most extreme situation, with very few supplies, except for three things: helpers, transport and moving boxes. Here are five easy ways to find the moving boxes for your relocation. Read through, and consider the easiest, cheapest, fastest or any other suitable solution for your move.

Online
Lots of Internet sites, starting with eBay and including plenty of similar sites where people try to sell and buy things.
Pros: Easy - you are just browsing the Internet at home, at work, on the bus or in the park. Convenient, too, because you receive what you ordered directly at your doorstep. It's normally fast because you can find and order the suitable boxes, but the delivery may take some time. Also, if you are lucky and/or persevering enough, you can get lots of boxes at a very good price.

Cons: If you are in a hurry and insist on immediate delivery, it can be more expensive. The biggest disadvantages are the time spent waiting for the supplies, and the fact that you cannot see the boxes before they are delivered to you. Also, if something is wrong, it will cost you lots of effort and time to get it straightened out.

Second-hand
Using second-hand moving boxes is cheap and environmentally friendly. You can get them from friends and neighbours who recently relocated, or you can use the local newspapers and/or message boards - either to contact a person selling used boxes or to post an advertisement and wait for them to call you.

Pros: As stated, cheap and earth-friendly.  
Cons: Takes some time; it might take longer if the number and sizes don't match your requirements; boxes could be torn or perforated or otherwise damaged; and you have to find time and a vehicle to arrange the transport to your home.

Convenient
You can spare yourself all the headache and time and buy boxes from a moving company. They have all possible sizes and types of boxes, and they deliver them to you.

Pros: Convenient, above all. And professional because that's what the company does, and you usually get advice on how to pack properly. You can also arrange with the company to have the boxes delivered in sets on different days, so you don't have to figure out where to put them before you use them.
Cons: The most expensive option.

Free
If your moving budget is tight, and you have the time and patience, you can get moving boxes for free from the local grocery or supermarket. They have all their goods delivered in boxes in every possible size, and they usually just throw them away. Just ask if you can take some of them and transport them to your place.

Pros: As stated, free of charge.

Cons: Besides the already mentioned energy and goodwill needed, not every box is suitable for moving - size, stability, soundness and available grips are the necessary requirements, but if you are close to desperate, you can make some compromises.    

Straight-forward
The place people normally buy moving boxes is the nearest big hardware store.
Pros: Enormous choice of sizes and types of boxes, and sometimes the big chains include delivery. You have everything else for the move in one place - wrapping, tape, gloves, tools, etc., so you can save time and do all the shopping at once.

Cons: Expensive, and you often need to make at least two trips to the store because you didn't get enough or because you forgot something.
     
After you are done reading, and if you still cannot decide which way is better, I would advise you to first, read again, and if you still don't know, just start anywhere. Plus, no one said only one option has to be selected - so try any combination of the above five!