I don’t know if you have found what you are looking for yet, but if not, take a look at the link below and/or do a search on eBay for “Marsee Tank Bag” for the different sizes and styles sold by “Liquid Performance“.
Marsee 12 Liter Tear Drop Tank Bag Expandable, Universal Fit, MAR-12DQR. The Marsee 12L Tank Bag has a contoured shape that makes it a natural fit for almost any. tank with a gradual slope. Universal Fit, EXCELLENT QUALITY!
www.ebay.com
I have been using Marsee bags for too many years to count. Top quality, in my opinion. Marsee stopped manufacturing these a couple of years back, and this guy must have bought their existing inventory and is now liquidating it. I would assume, when they are gone, they are gone. I have purchased two recently and am currently using the one with a plastic top, made for electronics, which I like a lot. The one in the link above is expandable, and really holds a lot for traveling. I used it on my VFR. Picture below:
Below is a picture of the one I am currently using on my RT and a link to it:
Marsee 10 L Teardrop w/Quick Release, Tank bag, Universal Fit, MAR-10DQR. Marsee's 10 and 15 Liter Tank Bags are triple layer molded for strength, flexibility, and water. The Marsee tray is designed to hold communication and electronic gear.
www.ebay.com