You must really love those rims and tires.
Can't find anyone to trade you smaller rims and tires? OK......
Getting a spring to give you an exact ride height is difficult because from what I can see, most of them simply give you a drop height from stock.
So honestly, your best solutions are: ( I don't care if you can do them or not for what ever reason, but these are ALL of your options )
1. Get some coilovers. They will allow you to adjust your ride height to what ever you want.
2. Get smaller rims and tires.
3. Buy cheap ebay sleeves so that you can adjust your ride height at the expense of comfort and reliability.
4. Buy different height springs until you find the one with the right height.
5. Do like what Lowered said and buy the stock springs and cut them to your desired height so that you can keep your precious 17" rims and tires that you have fallen in love with, that no one will trade with you for.
I don't think that anyone can come up with any other solution for you.
Where are you located? Maybe we can help you get rid of those 17's and help your mpg's with SMALLER rims.
Good luck.