I recommend Arcadia UVB bulbs over any other ones on the market. They will last for at least a year and if you have a meter to confirm the output they could go for 2 years plus.
As for fixtures. If you are upgrading your lights, I vote you go with a double HO T5 fixture with one 6% Arcadia and one 6.5K daylight bulb. That will provide the best lighting for both you chameleon and if you have live plants in your cage. I can send you some pictures of examples between just the single T8 fixture and a double T5. The lighting difference is amazing and you will want the double fixture for sure.
If you already have a T8 fixture and would just like to get an Acradic bulb to replace yours then the link posted above will work. However, I still recommend looking into a T5 fixture over the T8.
Feel free to hit me up if you have any questions or want some pictures.