Go to e-bay. Type in "fuel level sensor 2000 blazer"
Make sure to get the appropriate part (2 dr or 4 dr). The pump assemblies are different, so the sensor may be different too (not sure).
I replaced the sensor on my '97. You'll need to drop the tank to do it.
I ended up replacing the whole assembly a month later because I had a problem with the gasket (Oh, make sure you get a new assembly housing gasket too. I bought my sensor from GMpartsdirect, and it came with a new gasket)
'01 ZR2 Blazer, '97 LS Blazer, '94 FLSTC, '85 Corvette, '79 Civic, '04 Town&Country Family Truckster