In my own pocket change, I've found a single silver quarter (about 3 weeks ago) and 2 or 3 silver dimes; I've been searching for about 12 years now.
With roll searching, I've found one silver quarter and maybe 5 or 6 silver dimes.
I made out best by far working as a Cashier at a local Genuardi's (grocery store). They had very easy to check change dispensers; all I needed was the key to open them. I was nearly fired a few times for searching through them, but meh. I worked there for about two years, and over that time I've found:
- 94 silver dimes, 3 Mercuries
- 2 Buffalo nickels, one dateless
- 6 Silver war nickels
- Countless Wheat pennies, including a 1909-VDB and a 1943-S
- 5 40% silver half dollars (I was only paid with about 40 half dollars total; this silver / clad ratio was pretty good

)
- 8 silver quarters; most were 1964
That may sound like a good number of of silver quarters, but when it comes to the number of them I looked at, we're probably talking > 100000 quarters over the two years (they used up the most space in the change dispensers, so there were by far the most of them to look through).
To answer your question, there are still amazingly some silver quarters out there, but of silver nickels, dimes, quarters and half dollars, I'd say the quarters are the rarest.