There are a few ways to optimize opportunities to get shops. Make sure your profile with MSPs is set to receive email notifications of shops, then check email regularly. It will still be necessary to routinely check the job boards of MSPs. Keep track of the times of the month when MSPs post shops, especially the ones you want. They may post monthly, semi-monthly, or as needed. The end of the month is generally a time to hang by the computer as much as possible, starting around the 20th-25th, for the next month's shops.
JobSlinger's jobs will more than likely be unavailable. The advantage is you will find out which MSP has shops of interest to you, sign with the MSP, then watch.
No shortcuts. Lots of time with the computer. Self-assigns are very nice.