Pomp1

Heres a list borrowed from Ducatisti but I know of an even more complete list

Alternatives to the genuine Ducati parts
Here is a list of non-standard parts which have been suggested in good faith as alternatives to the genuine Ducati parts, which can be scarce, expensive, and some may be obsolete. Some information is only hearsay, so I cannot guarantee that the suggested part is actually going to fit. It is important to note that these suggestions have not been approved by anyone, certainly not the Ducati Factory who would presumably prohibit such fitment, void your warranty, and would possibly ban you from entry to their museum if they were to find out. If anyone decides to use non-standard components on their own bike it is of course entirely at their own risk in view of the lack of guarantees or assurances. If in doubt, seek the guidance of a qualified motorcycle engineer regarding the changes you are considering. The mentioning of any manufacturers should not be interpreted as an endorsement. Many of the parts listed are from foreign vehicles and while they may only be obtained from overseas, chances are that they may be easier to obtain (and a hell of a lot cheaper) than original Ducati parts.
If you have used alternative parts on your Ducati and can add to this list, your input would be greatly appreciated, and on the other hand, if you find any of the parts listed to be incorrect, please let me know, so I can amend the list accordingly.

Good luck!

Filters, air, oil and fuel
The air filter for the 1992-98 900ss/851/888 is the same as fitted to a Porsche 924. Dimensions are: 211 x 211 x 57. Purflex A515 (K & N equivalent: 33-2003, Mann-Hummel filter part number P12210).
Fuel filters: BMW K100RS part number: 13 32 1 461 265 (8mm) or 16142325859, Purolator F20011, AC GF61, Fram G2, Motorcraft FG-2, Wix 33032, CarQuest E2036 (mid-80's Ford Ranger. Fram part number G2). For the 916: Mahle KL 24/1, approximately 10-15 mm longer than the stock item, it has a 50mm diameter.
The 1994 750SS has a FIAAM FT 4648 fuel filter fitted as standard, here are some equivalents; A.L. ALG-6/8; Lautrette ELE1990; Chamption L101; Purolator F57608; Ryco/G.U.D MF-1; Fram G 12-1; Tecnocar B 7; GIF ES 77; UFI 31.001.00
Oil filters for belt-drive engines: same as fitted to Citroen 2CV & Peugeot 205 & 309 - UFI part number (23.105.00) corresponds with; AC Delco FX0011 (was X4A); Motorcraft EFL 47; Champion H101; NAPA: 1352 (1352NAPA and 551352 on the box); Cooper Z64; Powertrain FL125; Fiaam FT4654, FT 4847 or PA7059; Purflux LS187; Fram PH6074 (was PH2839, PH2864A); Purolator ML16829C (was FC 103 or OC 5); Halfords HOF216; Tecafilter Ref OC5; K & N KN-153; Technocar R12, R72, R434; Knecht OC 5 (equivalent to Ducati #065149960 and #090549960); TJ FB2094; Mann & H W712/9, W712/11; Unipart GFE 201.
Before using any of the above please be aware, early 650 Cagivas with Ducati engines sometimes do not accept the 2CV car filter, the threads differ. In this instance you will probably find that the following 3/4" UNF thread) will fit;
TJ filters: FB5311 and Fram: PH4482. The Fram filter is slightly longer and means you have to leave off the sump guard (Elefant), or make spacers.
Oil filters for bevel-twins: made by Meiwa for Kawasaki KLR250 & Z250 (Kawasaki part no. 16099-004 = Champion X310 and Fram CH6070) FBN OL1.01403.
GT Replacement Air Filters - 0615.27. 275 * FIAAM FL 6179 * FIAT Part # 4110530 * RYCO A134