The best Touhou crossover with Gundam is:
Reimu Hakurei and Unicorn Gundam/Full Armor Unicorn Gundam
Yukari Yakumo and Atlas Gundam/Full Armor Gundam
Marisa Kirisame and Banshee Norn Gundam/Banshee Gundam
Alice Margatroid and Silver Bullet

That's good recommendation for your next draw