I have a few of these VRBS ROMA types of Constantine and was looking on Amazon to see if there has been a monograph written about them. I was able to find a book with Vrbs Roma in the title, but I don't think it's about coins. I think it's about the city of Rome itself. Does anyone know if there's a book or good article (in The Celator, maybe?) about these? Constantine I, AD 307-337. Roman billon reduced centenionalis, 2.09 g, 17.4 mm, 1 h. Cyzicus, AD 331, 333-334. Obv: VRBS ROMA, bust of Roma, left, wearing plumed helmet and imperial cloak. Rev: Lupa Romana standing left, suckling the twins Romulus and Remus; two stars above; SMKS in exergue. Refs: RIC vii, p. 656, 91; LRBC I 1232; Cohen 17; RCV 16523. Here's the book I found. I'm not shelling out that kind of money unless it's about coins.
I don't know that book. I do know the Guido Bruck book has a nice section on these, with a graph showing all different types of reverse known for the type. Lucky for you, they redid this 1962 German book and translated it into English a few years ago. I would start there personally. You have to at least have a copy of that chart if you really love this type.
http://www.constantinethegreatcoins.com/comm/ Roman Collector, the above link illustrates 30 different examples of the VRBS ROMA type with the she-wolf suckling the twins.
This book gives the proceedings of a conference held in 1997 in the American Academy in Rome and the University of Rome "La Sapienza". Here are the contents: Introduction : Rome in late antiquity / W.V. Harris El inventario de Roma: Curiosum y Notitia / J. Arce L'edilizia pubblica a Roma in età tetrarchica / F. Coarelli Roma da Alarico a Teoderico / L. Pani Ermini Le domus tardoantiche di Roma come "sensori" delle transformazioni culturali e sociali / F. Guidobaldi La cristianizzazione della Domus dei Valerii sul Celio / B. Brenk La "biblioteca di Agapito" e la Basilica di Sant' Agnese / E. Giuliani and C. Pavolini The last pagans of Rome / Alan Cameron The Christianization of sacred time and sacred space / M. Salzman The populace of Rome in late antiquity : problems of classification and historical description / N. Purcell Canon Frumentarius, suarius, vianarius : stato e privati nell'approvvigionamento dell'Vrbs / E. Lo Cascio Rifornimenti urbani e cultura materiale tra Aureliano e Alarico / C. Panella I porti di Roma nel IV secolo / F. de Caprariis "Veniunt modo reges Romam" / A. Fraschetti Il Colosseo nel V secolo / S. Orlandi People as power : games, munificence and contested topography / R. Lim Conclusion / A. Giardina. Searching the content on the word "coin" returned 1 hit. Not the book you're looking for.