It took me about 3 weeks of refreshing an hour or so a day to attach a Moffit to my Plushie Slorg. I had about 30 items in my inventory. I even posted about it, asking if I was missing anything or doing anything wrong. It was my first petpetpet, so I was unsure.
Just keep refreshing. It is just a matter of time/luck. Some people get it in 10 minutes, some people refresh for a month! It's random. Keep at it. The good thing about all that time was a found a few codestones during all the F5-ing
Good luck!