Unfortunately, the original disc version of Rosenkreuzstilette has been out-of-print for years (naturally; the game first came out in 2007 and had a very limited print run - par for the course with doujin games, really...). Thankfully, the game has been re-released as a digital download, dubbed "Rosenkreuzstilette [erka:es] The Best", for 1,260 yen (~$15.30 USD) at DLsite.com: http://www.dlsite.com/eng/work/=/product_id/RE051185.html.
As for its 2012 follow-up: hard copies of Rosenkreuzstilette Freudenstachel can be purchased from J-Box for $36.00 USD. I've been shopping with them for years, so I can vouch for their reliability. They ship internationally, too: http://www.jbox.com/product/RKS002.
If you're a thrifty gamer or just prefer consistency in your game collection, you can also buy a digital version of Freudenstachel from DLsite.com for 1,365 yen (~$16.60 USD): http://www.dlsite.com/eng/work/=/product_id/RE102971.html.
Please keep in mind that our English translations are designed for these specific versions of the games. If you're having trouble setting them up, feel free to drop us a line and we'll try and give you a hand.
Thank you for being one of the good guys by supporting [erka:es]. Remember. the more support the circle gets, the higher the odds of us getting another sequel!