Hi,
Great frequent_flyer.
I bet one source for balsa in my country has light "Contest" balsa. The Company is "MBS RC Models" and they have some nice balsakits of "Viggen", "Saab 105", and "Draken". Also on "Tummelisa".
Skalamodeller (MBS) - MBS RC Models

They write this about their balsa sheets:
MBS RC Models balsa is of highest quality (AAA) and can be ordered according to weight below or according to own requirements (e-mail or phone for price info)
The balsa sheets are devided into 5 weight clesses:
1. Weightclass unsorted: a mix of all classes below.
2. Weightclass light: max 90 kg/m³
3. Weightclass light-medium: 91 – 125 kg/m³
4. Weightclass medium: 126 – 155 kg/m³
5. Weightclass hard: min 156 kg/m³

They have own laser cutter. So they can make "kits" from Cdr (Corel Draw), DXF (saved as version 14) and DWG files (not all versions).

I hope You can find proper balsa source for the Vortex kits. 2M F3A machines really need to be reasonably light so the pilot at last stage do not need hunt weight too hard when assembly start. I know too well the weight hunting circus that can start, and be expensive in worse case.

/Bo