What's wrong with checking the IGI on
www.familysearch.org, which is available online in England, France and Australia?
There's a William Wildman baptised in Ravensden on 12 June 1791, son of George and Ann, which might be him, but he seems on the young side to have married in 1808.
There was also an Ann Skinner Wildman, dau of the same couple, baptised in 1792, which may be a clue as to Ann, but I can't find a marriage for George and Ann.
However there are burials of
George 25 Jan 1793
Ann 2 Feb 1793
Anne Skinner 21 Feb 1793
William 23 Nov 1797
which may have been the entire family, but it would take the parish register transcript to confirm it. The transcript is available for purchase from either Beds FHS or BLARS. I think this William might be a red herring.
There's also a William Wildman age 62 buried at Ravensden on 8 Jun 1830, but I can't see a burial of Sarah, nor can I see her in a census. He appears to have been baptised in Ravensden on 29 May 1768, son of Edward & Mary. I wonder though if the 13 Sept 1808 marriage to Sarah Houghton may have been a second marriage for William, as there's a marriage in Ravensden on 25 May 1800 William Wildman/Ann Ravens and a burial of Ann Wildman on 27 May 1808. William and Ann baptised a number of children 15 Jun 1802-1 May 1808 in Ravensden. This would make William rather older than envisaged, and I suspect he was the William baptised 1768.
There were numerous Wildmen in Ravensden, so there's no reason that there should be a link with Riseley. Because he wasn't baptised in Riseley, despite being born there, doesn't mean he has to have been baptised elsewhere. He might not have been baptised at all. My understanding of the Riseley James Wildman was that he was possibly of non-conformist stock, which is why a baptism may not be found
In the 1803 Muster Roll there's only one mention of a Wildman in Ravensden - Edward who owned 1 cart, 2 horses and 1 driver. But there's a William Whiteman, tradesman, class 4 (unmarried men 50-55; married men over 30, married men 17-30 with more than 2 children under 10) which may be an error for Wildman. If it was really William Wildman he would have fitted in class 4 - married man over 30.
Virtually all of Beds baptisms and marriages pre 1812 have been extracted onto the IGI, so it is patently not the case that "research that far back is impossible online". Most of the above was done online. Of course information from the IGI should ideally be checked against the parish register, microfilm copies of which can be viewed at your nearest LDS Family History Centre, as the register will often include additional information
David