One of the great things about the internet and with eBay in particular is that due to the company being in existence in almost every corner of the globe you can find some very unique and interesting items that cannot be found in any other place. The key to finding collectibles and being able to buy them at a decent price is to take advantage of some little known tactics that many people don't know about.
One way to keep up with items that you are particularly interested in is to find the category on eBay and then add it to you favorites in your web browser so that you can easily keep up with it. Another thing that happens all the time is that sellers on eBay often make mistakes when selling an item or they may not know the real value of the item and will list it as just an average item when in fact it may actually be quite rare.
One caveat that I must offer is to not blindly believe that the description of something being sold on eBay is factual. I have seen many auctions advertise something as valuable, rare, or hard to find when they were really nothing special. Never bid on something that you do not have an idea of the value of. One thing that will save you a lot of time in your searches is to keep track of certain sellers whom you have found to always have the particular collectibles you are seeking, you can even contact them and ask them to email you if they get certain items.
Don't get wrapped up in the auction hype and think that if you don't win the item you will never have another chance. eBay is enormous and they have millions of items for sale everyday so the odds are that what you are looking for will become available again. You must never put yourself in a position of thinking that you must have an item, if you do you will end up paying too much. You must always be willing to let the item go if it brings a certain price so set a price that you think it is worth and if it goes above that you just let it go. I used to buy cars at auctions and I would have a figure that I was willing to pay for each car I bid on, if the price went above my figure I walked away and didn't look back.