In reply to Alien85:
Do you already have damage to fix, or are you looking for a repair kit "in case"?
Fabrics that are silicone coated on both sides have a very much higher tear strength than the same fabric coated with PU. Except for ultra light or very UV weakened fabrics, badly torn fabric is quite unlikely.
I spoke to one of the McNett Sales reps at the Outdoor show last year. We talked about repairing silicone coated fabrics, and using SilNet.
He told me that while SilNet is a great sealant, there is a limit to how strongly it can bond to a completely cured (and weathered/contaminated) silicone coating. Using it to glue on a patch is workable for very small patches, or in the short term. For larger / more durable repairs, he recommended sewing on the patch, and using Silnet as a sealant.
This limited adhesive strength may be true of other sealants/glues as well. It's also worth remembering that even at room temperature, it takes up to a day for the silicone to cure.
One source of matching tent fabric is often the original stuff sac. You could buy a second stuff sac that fits the tent and (when necessary) cut up the original for patch fabric. As Toerag said above, it's worth asking the manufacturer too.
If you are sewing silicone coated fabric, remember the yarns can slide over each other (this is the reason for its high tear resistance). This means that, like silk, stitching near the edge of the fabric can pull right out of the edge of the fabric. So leave 15mm or so to the edge of the fabric, use multiple rows of stitches if possible, and use a sealant like Silnet to help stick everything in place.
Silicone coated fabrics are incredibly slippery and hard to sew neatly, so for larger repairs it might be worth gluing the patch on with Silnet, sewing the patch on when the Silnet is completely dry, then sealing the stitching as a last step.
Hope this helps.