Hey Tom:
Although it doesn't specifically cover SCRs, the Haynes manual is best for
wide case Ducs. The factory (readily available as reprint) and Clymer book
an be helpful, but it's the Haynes I usually turn to. Sacn the net stores and Ebay for all. Also Motoscrubs (just Google it) has free parts manuals online for reference for narrow and wide case model SCRs. Very handy.
You didn't say what SCR you have, but there are three basic kinds:
250 narrow case
250~450 wide case Series 1
250~450 wide case Series 2
Narrow case will be obvious (250s only, ugly, but has its own charm [had one years ago]). Series 1 has steel rims, full gaiters on front/rear suspension. Series 2 equiped with alloy rims, double-sided front /Grimica brake, dust cups only front on forks, open springs rear shocks.
If wide case, check out
AMICI DELLO SCRAMBLER | Club Ufficiale Ducati Scrambler Rimini, Ricambi Ducati Scrambler Moto Epoca. Info you won't find anywhere else.
Hope this helps,
Cliff