You should be able to get a rebuild kit from any small engine shop. Lawn & Garden shops, saw shops, snowblower shops etc..

You will need to know the carb model #
It's located right next to the needles, or exactly on the opposite side from the needles. Usually a few letters and a number.
Examples:
HDA 137
WT 25
WA 174
Something like that. Give that ID number to the guy at the small engine shop and they should be able to get you a kit for it. They cost around $8--$15.

Be careful when you start to work on the side with the 4 small screws. Under that diaphragm is a metal lever that sits on a metal rod. It pivots back and forth on the metal rod. There is a tiny phillips screw that holds it all together. UNDER that lever is a teeny tiny spring. If you loose that spring-- your hosed --go buy a new carb. [] BE CAREFUL when you take that little screw out. Take it out slowly and move deliberately. Maybe even do this inside a ziploc bag in case the spring goes flying. It's very small and if it gets loose--it usually goes flying across the room and is all but impossible to find.

You need to take it out in order to replace the jet.