On the ww2.fighter.org website there is mention of two add-on CDs as well.
One by Swiper (the one we currently have) and I think it is safe to assume that the second Add-On CD was put together by "Aguada".
Although the old site had a link two download both Add-On CDs, the download link only displayed the first CD put together by Swiper:
If someone can contact Aguada, that might be the answer to finding the second CD.