Where can I purchase Charger and SIM card for my iPhone 8?

There is no such model as an iPhone 8GB. Go to Settings > General > About and see what model you have.

If this is a phone with 8Gb of storage, then that is a pretty old model and may not be worth it. Depending on which model it is it will either have a lightning port or 30 pin port. If it has a 30 pin port, your probably going to be out of luck finding a charging cable for it. If it has a lightning port, you can get charger and cables at an Apple store.

Finally, depending on which model it is, it may or may not be functional as a phone. You would get the SIM card by signing up with cell service from a cellular carrier. If it's very old and can only use 3G service, then it probably won't work as most cellular companies have shut that band off.

What type of charger you need will depend on what model of iPhone you have.

If your iPhone only has 8 GB of storage, that would suggest that it is one of the early, obsolete models that has a 30-pin Dock connector – perhaps the original iPhone, an iPhone 3G, or an iPhone 4s. I could be mistaken, but I don't see any iPhones later than the 4s that came with that amount of storage.

Those iPhones do not have 4G or 5G cellular radios – which means that there is almost nowhere in the U.S. where you can still get any cellular phone service for them. If you have one of these iPhones and you have the Dock-to-USB adapter cable, then you might be able to use it as a music-only iPod. But there's not much more you can do with it.

If I have misidentified your iPhone model, and you have an iPhone with a Lightning connector, please let us know that (and tell us which model you have).

There is no such thing as an iPhone 8 GB. Do you mean that you got an iPhone with 8 GB of storage?