If you're looking for a soft helmet to keep your headset in place, then you certainly don't need to wait six months. Numerous cloth and leather flying helmts are available, the primary use of which is to retain your headset (David Clark type) on your head during maneuvers. Cloth or leather helmets are fairly inexpensive, and you won't be waiting when you order. Try Chief's at
http://www.chiefaircraft.com/airsec/...htHelmets.html.
For leather, you might try Perrone Leather at
http://perroneapparel.com/store/helmets.htm
You can also get the David Clark conversion hard helmet that works with a headset. Try
http://www.chiefaircraft.com/cgi-bin...ashHelmet.html
If you're looking for a protective type helmet, then you should be able to get one immediately from a number of suppliers. Six months...no. However, they're going to cost.
I use the HGU-55/P type helmet, which is a lightweight Gentex model. Because of the high potential for the use of that helmet, I elected to go with Kevlar instead of the traditional fiberglass. The cost was higher, but it also vastly increases protetion from penetration through the helmet shell. I also elected to go with a leather interior using temperature sensitive foam, which makes for a much more comfortable helmet...an important consideration when you're wearing it for many hours each day. I also went with earcups with the oregon aero foam hush kit and leather earseals. You can get the typical helmets with the standard "elephant ear" interior which cost less, but the earcups provide better audio in my opinion.
How much you're willing to spend on the helmet makes a big difference. Mine was eight hundred or so, but I got a good deal because it came in bright yellow as an extra on a run made for a boat racing team...it was a clearance item. You can find the clearance items at Flight Suits Unlimited at
http://www.flightsuits.com/clear_helmets.html. You can get the helmet in a few days, if you want.
If you just want a hard helmet, you can get a motorcycle helmet, though don't depend on it for much comfort or protection, or necessarilly a proper fit and field of vision for flying.
You can also get used helmets and have them refurbished, if you like.
If you want a less expensive rebuilt military type helmet, you could try Government Sales at
http://www.aviationhelmets.com/helmet5.htm. Again, you're not going to need to wait six months.
Unless you're going with a close-fitting helicopter helmet like the HGU-84, I'd stay away from helicopter helmets. They tend to be heavier, loser fitting, and not compatible with fixed wing use. The SPH type helicopter helmets tend to be a little cooler on your head, but they're not as snug, and if you're flying something with a narrow canopy, they tend to be wider and bulkier.