Do you need wheels or are you using the stock 18/21?

 

With all the choppers running big front tires there are some quality 21" tires out there and almost any of them will stick well for street riding. I've even seen an XR600R supermoto'd using the stock 18/21 on it and outperforming some KTM supermotos, but that was the rider. I think he was running a Michelin ME33 at that time on the front, the back was a well worn Dunlop Sport Elite. If he can push them that hard a KLX250 should have no problem with a couple quality tires.

 

 

Click HERE and go shopping, a search for 21" tires at Bike Bandit. I'm sure others have them too.

 

I've used Shinko 705's and would recommend them even if it isn't really a "street" tire.
They hardly wore at all over 5000mi.
They can even get you down a dry trail if necessary, wet trails are less fun.