Try and get hold of a copy of "Breech Birth" by Benna Waites - there's a chapter in there about some of the reasons why babies are breech. It can be hereditary - I think she shows a family tree were something like 80% of people were breech - in which case it is most likely to do with the shape of the pelvis.
Other reasons that could cause a 2nd breech baby would include an unusually shaped uterus (bicornate or cornate - but you should know that from scans), or an unresolved asymetry in the mother's spine/pelvis (if you always sit with your legs crossed the same way, for example). If you think the latter might be possible, try and find a chiro skilled in the Webster Technique (or a good physio/osteo experienced with pregnant women).
I've seen some women say reflexology has worked for them, and there is some research that suggests hypnotherapy can be effective.
My DD was born as a breech baby at home with IMs. We didn't book the IMs till 36 weeks, so we knew she was breech and were able to choose our IMs accordingly - the NHS gave me a choice of CS or (when pushed) a very medicalised vaginal breech delivery and that did NOT appeal. What I didn't try was asking the midwives directly what their breech experience was - some NHS MWs do have strong skills in this area.
I don't know that breech increases the risk of a VBAC or vice versa. I don't know of any research considering this (but then I also haven't looked). The challenge is invariably finding the information - similarly I dont' think there's any research comparing the outcomes for vaginal breech birth with either vaginal breech delivery or CS, nevermind for women looking for a VBAC.
If you want to persue a VBAC my best advice would be to ask a LOT of questions (return to toddlerhood and go for "why?" at every opportunity ) and keep asking until you understand the answers. If start talking about research, ask for the reference (there are some papers out there that have been widely discredited but are still used to justify a CS - the Hannah et al "Term Breech Trial" being the prime example). Ask for an appointment with the Head of Midwifery and ask them the same kind of questions. And lastly, consider looking for IMs - they often have more experience in breech birth and VBAC (at least seperately) than their NHS counterparts.
Fingers crossed you can get your DC to turn, and good luck making a decision if they don't - its never easy and there's no single right answer, just one that's right for you and your family at the time.