Ruger still makes .454 Redhawks and they are common on the used market.
If you really don't want the .357 Redhawk, I'm sure a member here will give you a fair price for it. You can probably clear enough to pay for a used or even new .454 SRH and have a few bucks left over.
It took me over a year to locate a .357 Redhawk on Gunbroker and I haven't seen another one since. I love mine, but it's purely a range gun for me. I just wanted one for the cool factor.
Then again, Ruger stopped making .357 RH's for a reason, they didn't sell very well and most of them are in the hands of collectors or .357 enthusiasts who make wicked handloads. The guns have value to these buyers, and are getting to be more collectible as the numbers of them on the used market gets fewer and fewer.