Ive only caught 3. The first two were in March and justin said he would be doing shop restocks throughout the week. I refreshed every 5 mins over like 2 days.
Last and third time were the carnations.
Did you read Jacob's thread in the Bell Tree HQ? that explains how.
Basically the best way is to wait for restocks and hope you catch something good, or during events. Other then that using the VTP/trading plaza's works for small amounts. and of course, posting lol.