I get a TON of questions about the oval stamps I use in almost all the cards I make (I can't help it!! They never feel complete w/out them!!).
I have 2 sizes, a small one and a large one and I use *BOTH* of them a LOT - it usually depends on the sizes of the images I'm working w/ whether I use one or the other - but I couldn't live w/out either of them!!
The ovals are from A Muse (<---click on it and it will take you directly to their site) and you can see them both here (<---- click again and then scroll down a little till you see the "skinny oval bl" and "skinny oval bl sm" - those are them!!).
If you have a store in your area that sells A Muse stamps you can check there for these ovals and/or ask if they can order them in for you.
If you don't have a store locally that you can get them from (or like me you live in the middle of NOWHERE and have to have everything shipped in ROFL!!) you can call A Muse or fax in an order (the info is on their website) to them - they're super-nice to deal with. I called and told them what I wanted and it got shipped out to me w/in the next day or two.
Don't forget to check out their other stamps and accessories too - they have some really cute stuff!!
IF you do order - tell them AmyR sent you!! *grin*
ETA - I got more questions so here are the answers :o) :
Yes I stamp the main image first then mask it (I just use regular old sticky notes - you can see how I do that here) THEN stamp the ovals - it's really quite simple and easy. I keep my masks w/ the stamps they are for as I don't have the time to cut out a fresh one every time I need one.
*Most* of the A Muse stamps are rubber and wood mounted (and yes the ovals are rubber and wood mounted) - only a few of their stamps are clear acrylic (like their alphas) - and it says that w/ their description on the A Muse site.