For some time now it has been possible to purchase mod 0.3 gears from Didel in Switzerland, but not their gearboxes. The gearboxes are now available in "kit" form — meaning you assemble and provide your own motor — and in completely assembled form with various pager motors or one Portescap coreless micro motor installed. The gearboxes have been going through an evolutionary process and now use brass bearings or ball bearings depending on the requirements.
The gear boxes come in a variety of diameters allowing the use of pager, BitCharger, M20, N20, and a few other motors. They are also available in single and two-stage models depending on their gearing. The variety of gear ratios possible is pretty complete, and even more so if you supply your own Kenway 10t pinion to use in addition to the 12t Didel pinion.
The gears are very nice, and pretty much the lightest available. The only other mod 0.3 gears I know of this light are from servo gear sets (but the bore is often not what you want, and no 48t or 60t mod 0.3 gears are available in any of the servo gear sets I've bought).
Shipping to the US is pretty reasonable at about $4 or so, and it takes between 4 and 6 days. Eventually someone in the US will import these fantastic gears and gearboxes, but you can easily get them now direct from the manufacturer.
Jean-Daniel Nicoud, the owner, is great to work with. Check out his updated web site (which has some great pages on motor and prop characteristics and techniques for determining the optimal solution). He's very good and has a tremendous technical background.
The Didel web site is http://www.didel.com/Frames.html?MainFrame=NewsE.html
The email is firstname.lastname@example.org
There is no on-line ordering yet, but he takes credit cards. I've sent my credit card number in two separate emails with no problem. You can also fax it to him. So, order a supply of gears and gearboxes and motors today.