Step 1.
Look up these companies:
Cadence
Mentor Graphics
Synopsys
To find their competitors, you can look for their stocks on their respective stock exchanges, and then look for similar companies.
Step 2.
Visit their websites and look for investor information. In their public releases, they will (most likely) give a breakdown of how much of their revenue comes from EDA tools. Some of it will be from SPICE simulators; this part could get tricky. Apply some sort of wizardry to figure this part out.
Step 3.
Roll up some number and submit it to your government.
Although, from your statement that you're looking to implement some SPICE models for specific devices, it sounds more like the market you'll impact will be whoever uses those devices, rather than the SPICE makers. In that case, look for companies that play in that market and follow the procedure outlined above.