I actually make mine. I'm a photoshop preset maker, so it hasn't been a problem. But the more I'm into digiscrapping I realized how important shadowing is and how different it should be depending on the element used. Shadow must change depending on the element size (like weight and height, just imagine they're real objects and how the shadow is seen), the angle, and the effect you wanna give your page, for example I've learnt lots about shadowing by seeing Chris and Paige traditional scrapbooking pages and from Palvinka Designs, not sure if she gives her CT the shadows because, oh man, they create really beautiful pages.
I love using Tinci Templates they already include the shadows for each element, and yes they change depending if it's the paper, embelishment or the title. You should try her templates once
https://store.gingerscraps.net/Tinci-Designs/
Also Heartsrtings Scrap Art templates have shadows and believe me once you try replacing the clusters you're gonna love the effect those shadows give your layouts. How I wish she had moved to GS once Gotta Pixel shut down. I've got the daily downloads from GP and I still create my clusters off her templates lol (keep it a secret)
If I'm not wrong the in the lilypad and pixelscrapper you can find free shadowing presets, there's one at the first site but I have never ever used it. So I'm not sure if it works great. The second site has psd files for shadowing photos, they're great, they give different perspective to your pages.
This reminds me I started working on a tutorial back this Feb but I can't seem to finish it, translating and correcting my typos, maybe I just should share on my deviantart (linked on my signature) the style (.asl file) pack I did for the tut instead of finishing it first. Spring break is near so I might have the time to do it so.
I believe here at GingerScraps they don't sell shadowing presets, I lurked through the store for it a while ago and couldn't find any, that's why I gave other suggestions.
If you have a real fave shadowing recipe maybe you should make it a style or action (.atn file) for photoshop.