First off though, Bearbrick is not an action figure - it's an art / design toy! It looks like a Lego mini-figure but has no interlocking parts. Every Bearbrick is the same size, 1/8 scale (~5cm high) - but it can't just be reduced in size to get a smaller version! Bearbrick does not have interlocking pieces so you can't make your own designs by swapping heads and clothes either.
The first thing to note is that Bearbrick was originally designed by Takashi Murakami for Medicom. The first Bearbricks were produced in 2002 and it's still going strong today! Here are some of the common ways to collect Bearbrick:
Collect all designs - this is probably the most common way to do it, buy every new design as it comes out. This will take a long time as there are hundreds of designs! Collect all characters from a series - some of the most popular include the Mascots, Kaiju and Biopark ranges. Buy a specific design you like - this is what we do. It's not easy to decide on which design to buy first though, as there are a lot of ranges and it's hard to know which one will become the most popular. I generally go with Kaiju designs because they seem to be the most common around here in Japan. They also tend to be cheaper than other ranges, making them more budget-friendly.
To buy Bearbrick, you cannot just go to Toys R Us, brick-and-mortar store or shophomeless.com. This is one aspect that makes collecting them a challenge - it's not like Lego where you can pick up new sets on a weekly basis! In general, there are only two ways to get your hands on these:
There are many shops that sell Bearbrick in Japan, with some of the most popular being Donguri Kyowakoku and Kiddyland. Another good alternative for ordering online in English is Toys-Japan, although you'll need a forwarding service to get it shipped to your country. Bearbrick is also often sold at art / design / toy conventions such as Wonder Festival and ARTILLERY which happen twice a year in Tokyo and Osaka respectively.Finally, Bearbrick has become quite popular - even outside Japan! There are a lot of other stores outside Japan that sell Bearbrick too - and they can be quite pricy sometimes!