First off, KUDOS to you for trying to help take over care of the beardie. I know the whole lighting thing can be really confusing, so I will try to put it as simply as possible.
With 'tube lights', labels like t5, t8, or t12 help people determine size and brightness of a bulb. For example, a t5 light is going to be brighter than a t8 light. And if you have a light fixture for a t8 bulb, a t5 will not fit in it because they are different sizes.
Now in the reptile world, t5 and t8 also help determine the strength of UV that it puts out. UV is a type of light that helps reptiles use the calcium their body is receiving. If they didn't have this light, no matter how much calcium you fed them, it would basically all go right through them. When a beardie doesn't get enough calcium, it can cause them to be deformed, stunted growth, or other disorders, such as metabolic bone disease. Here is another good article to read if you are still confused:
http://www.lightyourreptiles.com/bulbs/arcadia/ .
Unfortunately many brands do not put out very good bulbs, and much of the time the reptiles end up getting inadequate lighting.
For those of us in the US, we always recommend the ReptiSun t5 10.0 bulb. For those outside the US, such as yourself, we recommend the Arcadia t5 12%. By just copying and pasting that name into your search browser, you should find many sights that sell just what you are looking for. Chances are your local pet store will not have what you need. Since I am from the US, i unfortunately cannot point you to any specific sellers, though hopefully some others will come along and help you out some more. Hope this helped!