where can I find experimental compressibility factor values?
The NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP) is a program that can calculate the thermodynamic and transport properties of some important fluids and their mixtures. It was developed by the National Institute of Standards and Technology (NIST) and is commercially available as NIST Standard Reference Database 23 here.

For example, the following selected results have been obtained with REFPROP Version 9.0. The number of digits is set to the default value (5 digits), which are not necessarily significant.

Methane
Temperature: 200.00 K
Pressure: 1.0000 bar
Comp. Factor: 0.99369
2nd Virial Coef.: −0.0065173 m³/kg
3rd Virial Coef.: 0.000015219 (m³/kg)²

Methane
Temperature: 287.00 K
Pressure: 1.0000 bar
Comp. Factor: 0.99802
2nd Virial Coef.: −0.0029520 m³/kg
3rd Virial Coef.: 0.000010232 (m³/kg)²

Carbon monoxide
Temperature: 200.00 K
Pressure: 1.0000 bar
Comp. Factor: 0.99739
2nd Virial Coef.: −0.0015501 m³/kg
3rd Virial Coef.: 0.0000035524 (m³/kg)²

Carbon monoxide
Temperature: 287.00 K
Pressure: 1.0000 bar
Comp. Factor: 0.99952
2nd Virial Coef.: −0.00040865 m³/kg
3rd Virial Coef.: 0.0000027781 (m³/kg)²

REFPROP can also be used to plot the results, for example for carbon monoxide: