Hi ba-tex,
I found the NMR-100C at Digikey (You are not allowed to view links.
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Login) their part number is 811-1566-5-ND, and they say they have 59 in stock.
For the 6N137-000E, I looked for a replacement and found HCPL-2601-000E (Mouser p/n 630-HCPL-2601-000E). Looks to be a "better than" binning of the 6N137 with better common mode rejection (and a slightly higher price). You can find the datasheet for it here: You are not allowed to view links.
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Login. See page 2 for the comparison between the different part numbers. Mouser reports to have plenty of these on-hand.
Oh, and I should mention, I just ordered these last night, so can't *guarantee* that they are available, work, etc. Just wanted to share what I'd found...
Good luck.
--Dave