Lagunitas makes this exceptionally cheap ($3.49/22 oz. bottle) double IPA. Lagunitas loves making hoppy beers, even their pale ale is hoppier than a standard pale ale, so you know this one's going to be packed. But at $3.49, you do get what you pay for. It's pretty much hops, hops and more hops without the sweet malt to balance them out. You'll know you're drinking hops, but it's unclear that you're drinking a double IPA because the sweetness normally associated with a double IPA isn't there. It's a good beer and a great value but not quite the accomplishment that Hopslam or the next 2 beers are.
A Little Sumpin Extra! Ale
This one is also made by Lagunitas. It has a little more maltiness and sweetness and a little less hoppy flavor of the Hop Stoopid. It's a little more in line from what I'm looking for in a double IPA. It's also a little more expensive than Hop Stoopid. It is a seasonal so it might be a little harder to find than the Hop Stoopid which is a big seller I think because it is so cheap and has a more gimmicky name. Little Sumpin Extra is aptly named because that little sumpin is a better balance, more alcohol (8.74% ABV) and is just a more pleasurable drinking experience.
I've raved about Avery's Maharaja before and I'll do it again. It's one of my favorite beers and it's the first double IPA I liked (they're usually too sweet for me). Everything about it rings perfect to me. At 10.24% ABV it's also a beer you can't drink all the time giving you that special event feel every time you have it. Again, this one is a little more expensive around $8/bomber but it's a good deal. If you only have one double IPA (available in KC) this year and it's not Hopslam, it better damn sure be Maharaja. I think the Maharaja is pretty close to the equal of Hopslam AND it requires little to no effort to find.
All 3 of these replacement double IPA's can be found in any liquor store that carries bombers and has a decent selection. I'm sure others have a double IPA that they like more than the 3 I've mentioned, but these are the 3 I've tried and liked. Also, as you find Hopslam in stores or on tap shout it out in comments to help out others. You've got yours, why not help others reach a hoppy bliss?