What if there was a model that spanned the United States?
I decided to use the distance from San Francisco to Washington DC as a base length of 3932km (from Wolfram Alpha).
Then I took the average AU distance of the planets (ending at Neptune) as a percentage and converted that to km in the SF to DC distance.
Here is the spreadsheet I made for the data.
I used Google Earth to estimate the location of each planet in the US.
Here is the map of the points on Google Maps.
View US Scale Solar system in a larger map
Calculating the ratio of scale km to real km turns out to be
1 km:1.14x106 km
Scaling the planets according to this ratio (also on the spreadsheet) unfortunately results in a 1,200m diameter sun in SF. The most practical way would probably be to use a different scale for the planets, and use a 1.2m (diameter) sun in SF, and a 4cm mercury.
Yes, I did post this on Reddit first, to make sure my math was correct.