Some of my GoTo Vendors

Framers Inventory, picture frame moulding and framing materials.
Portland owned and for wholesale customers only
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Larson Juhl picture frame supplier.  Explore design options with the LJ design studio

Roma Molding, picture frame supplier - made in Italy mouldings

I also carry Nurre Caxton, Nielsen Metal Frames, Omega, Picture Woods,
Munn Frameworks, and several others

Closed Corner (Museum frames) I carry APF Munn, AMCI, C & J Picture Frame lines.  If you look closely at these frames there is no visible corner seam and they are often hand carved.  These frames are built to my client specifications:  different metals, colors, depths, rabbit depths and can be infinitely customized.  They also take four plus weeks as they are built from scratch.

Below are just the tip of the closed corner iceberg of frames.
in this case I used the C & J site as their pictures were generous and large enough to see details.