We're not talking about kebabs, you know
If you have a history of major giving at your organisation, then the most obvious first step to take is to do a search on your database for previous major donors. After all, there is no reason why a previous major donor should not be a future donor, given the right approach, especially if the donation was not recent.
If you want to be really keen, you can go several steps further than that, depending upon the history of your organisation and the resources at your disposal.
When I was the researcher at Great Ormond Street Hospital I decided (due to a rush of blood to the head, no doubt) to compile a list of all major and significant donors to the hospital from its foundation in 1852 to the present day. (By significant, I mean well known or notable in some way. Celebs, politicians, that sort of thing.)
Of course, there were no databases in the 'good old days' of Charles Dickens (who was one of the significant donors) and so a considerable amount of real research was required (i.e. not just logging on to that interweb thingy, like you youngsters do today). I read books and articles on the history of the hospital, waded through various newspaper cuttings and other archive material in the hospital museum, and sifted through reams of faded computer printouts kept by the Finance Department from the days of the Wishing Well Appeal. Some very interesting names came up.
is so stupid as to repeat such an exercise themselves has such archived material available to them, but you never know what useful information may be available (past annual reports, old newsletters, etc.) or who you may uncover, unless you look for it.
And if a past major donor is now deceased, then why not add his or her surviving relatives to your pool of prospects?
If your search brings up few prospects, then simply expand your search.
Look for donors who have given a one off gift of between, say, £1000 and £9999. Or whatever values you wish. You want to produce a manageable list of prospects, somewhere between 25 and 50, say, so if you get much more than 50 names I would up the minimum donation to £5000 to produce a shorter list.
Then do another search for those who currently give, say, a regular gift totalling £500 per year. Again, use whatever values you wish to produce a manageable list.
This will produce two lists of prospects who may be capable of making a larger donation. At this stage, of course, you simply do not know, as all we have are two lists of moderate donors. Further research will be required to determine the wealth of these prospects (hence the need to keep the list to a manageable length.)