This doesn't directly answer the question, but is, I believe, a good alternate:
Since you've already got the wheel/rim disassembled, I'd suggest taking the tire (bring the rim with you, just for fun) to a couple of local big-box hardware stores and see if you can find a replacement that matches*. If you can't find one there, try a local lawn-mower repair guy - he's bound to have and/or know where to get a replacement tire that'll work just fine.
Actually, I'd suggest going to your local lawn-mower repair guy first, just to help support a local business. You may pay a couple of dollars more, but (most likely) get great knowledge and service. He may even remount the tire for you at low/no charge. And he may get you going today instead of waiting for something to ship to you.
Worst case scenario, he'll tell you you need to order directly from McCulloch/Huskvarna directly, but he'll likely know which one will work.
* by "matches" I mean rim diameter & width and overall tire circumference. You need to be able to mount the new tire to the rim without it rolling off, and you want the same rolling diameter on both sides of the axle or you'll be steering in one direction just to go straight. If you absolutely cannot find one with the right outside circumference, you may need to buy two (if they're not terribly expensive) and replace both front tires, or bite the bullet and get the OEM part. I can't imagine that there are too many varieties of lawn mower tires, but, who knows...