Eternabond, is usually available at Roofing supply houses. ABC Supply, Allied Building, etc. I'm not familiar with the SF area but you should be able to find one.
You also shouldn't have too much trouble getting it either, Eternabond is primarily a roofing product but it's also used by other trades.
Is this on a shingle roof?
If so I would recommend the pitch pad/tape. Better yet, roofing cement.
Locate the mounting positions of the main bracket and the mono poles. Spread a layer of roofing cement on the those areas about an 1/8" thick, overlapping about 2" around the bolt holes. then apply a layer of reinforcing cloth, (sold right next to the roofing cement usually a 4" wide roll.) then another 1/8" layer of cement.
Install the mounting pads. with the proper lag bolts. If it makes you feel better cover the bolt heads overlapping onto the bracket.
The roof cement is available in standard caulk tubes at any home center.
I'm not an installer, I'm a commercial roofing estimator.
The Eternabond is a great product for low slope (flat) roofing membranes and flashing into them.
It really won't stick too well to the granulated shingles.
One other thing.... DO NOT use Silicone on your roof. The stuff is great for windows and counter tops, not asphalt based roofing products.
Good Luck!
