You don't currently have a 'settlement visa', you have a spousal visa, and it is settlement you are going for.
As your visa was issued by an entry clearance office (if it was issued out of the UK) you won't have a Home Office reference. If you switched from a fiancee visa, then it will be the number on the approval letter, usually a letter then seven numbers.
Think about your first year here, very carefully, and think about what you did. Did you register with a doctor, open a bank account, get a credit card, register for council tax, did any of your family write to you and have you kept the envelopes? Did you register with the US Embassy, or get your name on any of the bills? Did you apply for jobs or get an NI number?
There is no way around this...if you really can't get any documents for the first year, then they will just grant you another extension instead of giving you indefinite leave. But I am sure if you think you will find something. There is more leeway on this than people realise.
Vicky