Dear list members,
For those who have been following the thread, a mantra to Dhanvantari in a medieval text has now been found, Thru Dr. Vigneshwar Bhat who suggested to a colleague that there is a mantra to Dhanvantari in  prapañcasāsaṁgraha,. thru Elaine Fisher who ocorrectly identified the text as  prapañcasārasārasaṁgraha by Gīrvāṇendra ṣarasvati, and thru Mohan Chettoor on the Samskrita list who found the mantra on page 778 of   part II of prapañcasārasārasaṁgraha by Gīrvāṇendra ṣarasvati.  https://archive.org/details/in.ernet.dli.2015.311363
Again if its of interest to anyone the mantra from the book:

atha mṛtyuñjayamantraprasaṅgāt mantrasārokto 
rogaśāntikaradhanvantarimantro'pi likhyate-
apāntaratamā ṛṣiḥ । triṣṭupchandaḥ । dhanvantarir devatā । oṁ bījam । svāhā śaktiḥ । sarvarogavināśanārthe viniyogaḥ । oṁ namo bhagavate hRt । dhanvantaraye śiraḥ । amṛtakalaśahastāya śikhā । sarvāmayavināśanāya kavacam । trilokanāthāya netram । viṣṇave svāhā astram ॥ 

dhyānam --śaṅkhaṁ cakraṁ jalūkāṁ dadhadamṛtaghaṭaṁ cāpi dorbhiścaturbhiḥsūkṣmasvacchātihṛdyāṁśukaparivilasanmaulimambhojanetram । kālāmbhodojvalāṅgaṁ kaṭitaṭavilasaccārupītāmbarāḍhyaṁvande dhanvantariṁ taṁ nikhilagadavanaprauḍhadāvāgnilīlam oṁ namo bhagavate dhanvantaraye amṛtakalaśahastāya sarvāmayavināśanāya trilokanāthāya viṣṇave svāhā । ityekacatvāriṁśadakṣaro mantraḥ ।।


Harry Spier