RMI-25 has been used mainly in the industrial/commercial market for over 25 years. Only recently has it been brought into the general automotive area. It is distributed through dealers and reps that are familiar with the product.
In a chain store it would compete on a shelf with many inferior similar products which sell at a lower price. Since "cheaper" or "cheapest" is what the general un-informed consumers buys, RMI would not be a big seller.
Why not support Buick vendors that carry it? Ones that come to mind are Jack Cotton, Ron's Custom Auto, O.G.S. and Jay's GN.