When I bought the bike the front slider had some chain grooves in it, so I have no idea what they look like new. Are they as simple as its worn out when the chain is almost touching the rivet head? Also does the guide on the rear have a replaceable but or do you have to buy the whole peice?

 

The individual parts are replaceable but it's a shed load cheaper to by aftermarket. I bought a Moose Racing chain guide for less than the one piece I needed of the OEM chain guide for my KDX200.
Check out www.Partzilla.com (or many others) for part numbers and prices of the piece you need.
Check out places like http://www.motorcycle-superstore.com/ you can put in whatever bike you have and it will tell you what bits fit.
If you wan't advice on your specific bike tell what it is including what year and show photos of the parts.