(By the way, as I've told my classes, if you choose to make beads with a "reliquary" pendant for replica purposes you certainly don't have to use an actual saint's relic. I know many modern people are uncomfortable with the concept of religious relics for one reason or another. A personal keepsake, such as a lock of hair, seems to me to be a pretty good substitute.)
I've also been corresponding with a couple of jewelry makers who are (FINALLY!) working from period paintings to produce actual replicas of the 1" to 2" pierced pendants visible in paintings. (If any of you are reading this, you're welcome to provide links in the Comments.) Unfortunately for me, while the ones I've seen are quite splendid, most of them are silver or gold and out of my price range at the moment. (I received a very nice little silver egg-shaped pierced pendant as a Twelfth Night gift last year -- thanks again, H.) I can certainly understand why jewelers would go for these, since I think it's the same amount of work to make something in silver or gold as it is to make the same thing in pewter, and I suspect the precious metal version is more profitable.
For those of us who do everything in pewter, however, I got a sale catalog from Fire Mountain that contains a couple of candidates for pendants that might be at least plausible for the Middle Ages or Renaissance:
Large pewter "heart" cage (18x18mm) with heart shaped piercings
IMHO, this one isn't as period looking as the smaller one below. I don't recall having seen heart-shaped piercings on any period pieces, but it's certainly a shape that was well known for brooches and other jewelry. Unfortunately the hearts on this one are randomly oriented on the back of the "cage," which is something I wouldn't expect with a medieval esthetic.
The small version OTOH (and it's quite small, about 1/2 by 3/4 inch), has round- or scallop-shaped piercings that more or less follow the shape of the object. I haven't seen a medieval heart shape that is quite as short from top to point (compared to the width) as this example -- most of the medieval hearts I've seen are taller and skinnier than modern hearts, if anything -- but I'm a lot less bothered by that.
Small pewter "heart" cage (16x13mm) with round piercings
If you do a general search for "cage" on the Fire Mountain site, you'll come up with about 40 links and drops of various sizes. Most of them have wide spaced vertical bars, which makes them easy to insert something into, but not so suitable for most "relics," since whatever is in there has to be fairly large in order to be securely held. They could, however, probably be filled with scented resin or something else that will stay put. Here's a pierced bead from a replica I made that uses a paste of benzoin and gum arabic inside the pierced metal beads. (I chose not to use a wax-based filling, BTW, because I live in California, and I don't want to risk wax melting all over something in the summer!)
Awhile back, Fire Mountain was also selling larger, flat cages they were calling "bead keepers" -- hinged containers about an inch and a half across, with woven wire backs and pierced or woven metal fronts. There are round, square and teardrop-shaped versions of these, but the square and teardrop shaped ones look very modern. The round one, OTOH, has pointed oval and quatrefoil shaped piercings and I think could reasonably pass as a period artifact. I think these are now being discontinued, so if you want one, now's the time to get it. The last I checked, they seem to be out of the silver-plated version but still have the gold-plated one.