What a coincidence that this thread came up again, had the same conversation on Facebook just a few minutes back where I talked about this.
My close sheltie friend told me not to use Trifexis as well. The risks just seem to prevalent compared to other well known brands. If I had to choose, I too would choose Revolution first. However, it just didn't make sense for me to do that for 6 months when she'd only need protection possibly against ticks in a not tick problem area anyways for less than a week. So instead I decided to continue my search for Sentinel and use Neem oil or a tick collar during the time when I'd need it for an outdoorsy day, and wanted extra protection. Also, I sleep with Precious alot and bathe her a lot when needed and a topical just didn't feel right for our usage in fear that it'd just rub right off and Precious wouldn't get the full treatment needed. I really do prefer orals for dogs.
This is what I wrote on facebook: "I remember we had this problem in the beginning of May when I started my search as well. After much headache and many phonecalls, we did find another vet in the area (good reviews, great clinic, I felt it was a safe place to buy Sentinel from). However, right after my vet found out that we wanted to purchase from another place, they 'all of a sudden' found two extra pills for us in Precious' weight and told me to take these and then by July, they should have more because it's expected that production should have continued by then. SO long story short, try to squeeze it out of the vets. They knew I wasn't willing to try Trifexis OR Revolution. And they didn't think I'd go so far as calling 30 other vets to try and find it either. So when they figured out I was serious, they gave me the last few they 'actually' had while others changed to a different medication. All I can say is... Best of luck and keep looking! You'll surely find it!
I had a sheltie friend who shared this with me a few weeks ago. Said Dee was a sheltie breeder as well so this applied to shelties.
http://www.facebook.com/dee.silverstein.7/posts/4098475384426
Of course, all medications always have the risk of side effects and there's always a risk. But I am comfortable with what works for my dogs and don't really like changes, especially with this new drug that is only in Canada as a temporary replacement and no real known history/facts at the clinics from where I'm from. Feel free to read it

"
That's all the information I have as an update for now. Hope it helps some and hope you keep looking. If not, I recommend Revolution as it was next in line for me as well if I couldn't end up finding my Sentinel (which I did).


GOOD LUCK!