Hello all!

I have Home Legend # HL16H Hand Scraped Oak Gunstock 3/8 in. x 4-3/4 in. Engineered Click Lock Hardwood Flooring. The manufacturer offers two approved installation methods under their warranty...Primary is "Floating" or alternately "Full Spread Glue-down".

I'm planning a floating installation over a 2nd story plywood subfloor. I understand, a floating install typically calls for an "overlap stair nose", where the floating floor meets with the top of a staircase landing so the flooring will float under the stair nose, leaving the required expansion gap. Unfortunately, Home Legend does not offer an "overlap stair nose".

Where can I get a 3/8" "overlap stair nose" to use with this flooring?

Your best bst would be to try and find a nosing for a 5/8th inch thick floating floor and then use a table saw to rip it to your floor thickness.

What about something like this, which doesn't appear to be engineered and I'd have to stain it to match?
http://www.lumberliquidators.com/ll/c/xUnfinished-Oak-Overlap-Stair-Nose-UNROOVSN38/10026286

You may get a good one if you can choose one with the same type of grain pattern as your flooring. Try stain samples on the underside.
You will notice over time that the finish that you put on it will wear out a lot faster than the finish on your flooring.

It's apparently not in stock locally and I'd have to order it blind.
This stair nose can be re-finished, if needed, correct?

Some nosings are just medium density fiber board with a veneer covering it.Solid wood will be good for many re-finishings. When it starts to get worn you can re-coat the finish if you take care. Sanding to bare wood you can change the color.If your stain color doesn't match perfectly you can add color to some finishes. Be careful to not get the stain color too dark, the wood deepens in color over time.