Answer: Thank you for asking but in a brief search unfortunately I am only able to locate one nursery showing it in the US (sources I am seeing are in the UK or Europe) -- it is located in Delaware and it is not a mail order nursery although their web site says they occasionally ship.
To be honest I am not sure that the plant you have is truly a cultivar of Euonymus japonicus. The reason I am wondering is that E. japonicus is usually only considered reliably hardy into zone 7 and your zip code places you in zone 5A, the coldest part of zone 5. That is a big difference in climate. You might want to take a sample or two and try to match it against other plants offered for sale in your area, or check with your county extension or a professionally certified nurseryman, just to be sure. (There are a number of gold variegated varieties of Euonymus fortunei that would be hardy in your area.)
There are hundreds of different euonymus cultivars on the market so if you can't make an exact match perhaps you can find something similar to what you already have. The other possibility would be to root tip cuttings and propagate more yourself (or ask a nursery to do it for you) -- this would be an exact match although it might take a few years to produce good sized plants.
I'm sorry I couldn't find an exact and convenient source for you.
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