Remote sensing of the simple (few atoms) greenhouse gases works by comparing the measurement spectra with calculated spectra. These calculations are very precise and probably the reason why you do not find so many measured reference spectra.
The reason for calculation is that the atmosphere has pressure, concentration and temperature gradients which even depend on path angle(s). So sensing by comparison with lab-measured spectra requires many spectra under different conditions and sophisticated interpolation schemes (Which is nevertheless done for the more complex greenhouse gases or the HFCs)
One important database for greenhouse gases is HITRAN. Since the simulation code is not so trivial to implement I would suggest you to use a website which does the calculation for you. e.g.:
Spectral Calc or HITRAN on the Web
There you enter your gas parameters (pressure, temperature, concentration, path-length) and so on, and it will calculate the spectrum in (almost) any wavelength range for you. Of course the accuracy may vary with wavelength range, there you would need to check the accompanying literature. Nevertheless, the strong absorption bands of the greenhouse gases are well researched and the data is of high accuracy. E.g. for the 4.3 µm absorption band of $CO_2$ we probably have the best researched spectral data of all gases, with accuracy of probably better than 1% if not 0.1 %.
For the more complex molecules, where a line-by-line simulation is not available, you find high-quality measured spectra on the HITRAN website (-> "Absorption cross sections")