So far, it seems that DVD writers that support Mt. Rainier are few and far between - VERY far between ... I have a vague recollection that there might have been one, but not a slimline - it's poften said that many of the chipsets ARE capable, just that the makers seems to have turned their back on this useful standard.
The official list is very small indeed:
1. Philips DVDR1640 firmware version MR11
DVD+RW/CD-RW drive produced by Royal Philips Electronics, The Netherlands.
2. NEC ND-2500A firmware version 1.0M
DVD+RW/CD-RW drive produced by NEC Corporation, Japan.
3. Sony DW-R56A firmware version NDT1
DVD+RW/CD-RW drive produced by Sony Corporation, Japan.
Not even sure if the supporting versions of those are actually generally available.
Mount Rainier on CD-RW had a fair degree of success, but the manufacturer apathy to it in their DVD writers is disgraceful