So sad. Another “national Tea Party convention” cancelled due to lack of interest… and funding, since it was billed as a true grassroots-organized event not supported by one of the AstroTurf groups that pay for the buses and the wall-to-wall FOX News coverage. Organizers of the Freedom Jamboree announced Wednesday that they have canceled the tea party convention planned for this fall, citing low registration. They had hoped the event would serve as a stage for Republican presidential candidates to court the conservative movement, and two — Rep. Michele Bachmann Minn. and former Sen. Rick Santorum Pa. — had already…