Good morning, Terry;
The Silver-Oxide batteries have a much more stable discharge curve. Their voltage stays nearly the same over their useful life. Not exactly, but similar to the old Mercury battery, but at a slightly higher voltage. The alkaline batteries will have a constantly decreasing voltage that will affect the light meter reading by a constantly changing amount. At least with the Wien cells and the Silver-Oxide batteries, if the light meter reading is off, it will be off by a fairly predictable amount, so you can compensate if required. Often the lightmeter circuit can be adjusted to work with the 1.55 VDC batteries.
There are many sources for Schottky Barrier Diodes. Radio Shack did have them in the past. Jameco Electronics. Digikey. All Electronics Corporation. RF Parts. Mouser Electronics. Ocean State Electronics. Frye's Electronics. Newark Electronics is still there, but the minimum order amount may not be palatable. There are still people who are selling bits and pieces.