Hi Darren,
I had a search of the Western Australian BDM index and found no records for William's marriage or death. You can search the site yourself at:
http://www.justice.wa.gov.au/portal/server.pt/gateway/PTARGS_0_2_323_201_0_43/http;/justicecontent.extranet.justice.wa.gov.au/bdm/default.asp?structureID=96554822&ResourceID=295610339To try spelling variations, type in part of a surname followed immediately by an *. I did try that myself but still came up without a result.
These were the results for a search of "William Markham" in New South Wales:
(index no., surname, first name, father's first name, mother's first name, where died)
8000/1906, MARKHAM WILLIAM, THOMAS H HANORAH, BELLINGEN
15670/1893, MARKHAM WILLIAM, HENRY ELIZABETH, WOLLONGONG
11961/1882, MARKHAM WILLIAM, WILLIAM, DIED SHOALHAVEN SHOALHAVEN
9306/1885, MARKHAM WILLIAM G, WILLIAM ELEANOR A, LIVERPOOL
8734/1945, MARKHAM WILLIAM AUGUSTINE, JAMES ELLEN, COWRA
18670/1924, MARKHAM WILLIAM, WILLIAM JANE, GRANVILLE
12171/1925, MARKHAM WILLIAM, CHARLES WINIFRED, WOLLONGONG
15520/1922, MARKHAM WILLIAM, THOMAS SARAH, GRANVILLE
11877/1942, MARKHAM WILLIAM, WILLIAM MARY, NOWRA
14597/1942, MARKHAM WILLIAM HENRY, JAMES MARGARET, SYDNEY
You can do a search of Victoria's historical index yourself at the following site:
https://online.justice.vic.gov.au/servlet/IdxSearch?action=gotoPrePaySecure(suggest putting in a spending limit of AUS$1.00 at a time ... it costs 99c for each page of records found)
I also searched Tasmania to 1899 with no result. I don't have the indexes for South Australia or Queensland and they are not available online.
Good luck in your search.
Cheers, Brisgirl