Dear Rebecca,
Let me wish you a happy new year.
In fact, the written available version of ISO 639-6, First edition, 200-12-01, contains strictly no official list of alpha-4 ISO 639-6 code elements.
Only Annex A (informative)  "Example data"  gives a Table A.1-Nilo-Saharan (part) Saharan (part-exemple data only) containing 56 alpha-4 code elements, each given with an alpha-4 "parent identifier" and a "Language reference name".
The standard also writes that "at the time of the present publication of this part of ISO 639, the ISO 639-6 Registration Authority (ISO 639-6/RA) is held by:
Geolang Ltd,
 the URL of the website is".
ISO 639-6's clause 8 "Administration of code assignments" writes that "the allocation of alpha-4 identifiers shall be administered by the ISO 639-6 Registration Authority".
It is nowhere explicitely written inside this standard, but it is natural to think that the web site for the ISO 639-6/RA is where the  current ISO 639-6 code list is to be found.
But, in fact, the only available information I found on this site is "Currently ISO FDIS 639-6 is being prepared for FDIS vote."
So that the best available source" for comprehensive coverage of language variants" remains the principal source of ISO 639-6:
"Linguaspere Register of the World's Languages and Speech Communities: hebron (Wales) Linguasphere Press 200. 2 vol. ISBN 0-9532919-1-X, ISBN 0-9532919-2-8"
Whose author, David DALBY, was the initiator and first conceptor of ISO 639-6 as presented at the 15th plenary meeting of ISO/TC 37 in PARIS in August 2004, when the corresponding New Work Item was adopted, after a first presentation  by "The Linguaspere Observatory" of the british standard BS 8639 - Identification and Classification of the World's Languages and Communities including CLIP (Community and Language Identification Protocol) at the week meeting of ISO/TC 37 in Oslo in August 2003.
David DALBY is still developping his work, that remùains by far the more interesting system in this domain.
You will find attached with this message, my note 55.2009.doc, written in french language, that could nevertheless have some interest for you.
Bien cordialement.
Gérard LANG
-----Message d'origine-----
De : ISO 639 Joint Advisory Committee [mailto:[log in to unmask]] De la part de Rebecca S Guenther
Envoyé : lundi 4 janvier 2010 22:07
À : [log in to unmask]
Objet : Re: ISO 639-6 is available

Could you tell me how many codes there are in this list (although I understand that it will be growing)? I am giving a presentation on the ISO 639 standards to the Linguistics Society of America on Friday and would like to have this information. (I suppose it is available on the ISO members site, but couldn't remember my login information.)


>>> Lang Gérard <[log in to unmask]> 12/3/2009 2:36 AM >>>
Dear All,

The first edition of ISO 639-6 (Codes pour la représentation des noms de langues-Partie 6: Code alpha-4 pour un traitement exhaustif des variantes linguistiques // Codes for the representation of names of languages-Part 6: Alpha-4 code for comprehensive coverage of language
variants) has now been published by ISO, effective from 2009-12-01 on.
Gérard LANG