I love updisde down lily flowers but have not had much luck with martagons (it may be too wet here). I have substituted Lilium 'Citronelle', Lilium 'Pardalinum' and an old fashioned orange tiger lily with upside down blooms to get a similar effect.
Please let me know if there are other lilies out there with this habit. Thanks.
Lilium 'Citronelle' single
Lilium 'Citronelle' cluster