Its difficult to get durva by me so what else can be offered to Ganesh ji, instead of durva.
What we offer to the deities is called UpachAra. When a particular UpachAra can not be arranged for, then a substitute (anukalpa) is always prescribed.
Quoting from Anhika Kritya (by ShyAmA Charan Kavi-Ratna VAridhi), first BhAga, 1st Khanda (p 30):
Substitute for honey (madhu) is jaggery; for ghee it is sesame oil; for all things it is jaba (barley); substitute for all flowers is DurvA or Atapa tandul (unbroken rice or akshata); substitute for all kinds of musical instruments is GhantA (bell) substitute for all UpachAras is water (udaka).
In his support, the author quotes verses from two sources. Given below is one such verse from the Nrisimha PurAna, which states that, in the absence of any UpAchAra, water can be offered instead.
alAbhe sarva-dravyAnAm udakenApi pujitAha (One must worship with water instead when any other ingredient is missing) |
Yo dadAti swakam sthAnam sa tvayA kim na pujitah || (Nrisimha PurAna).
So, you can say "nAnAvidha parimala patra-pushpAni arthe (artham) udakam samarpayami" (I'm offering water in place of various fresh flowers and leaves) or more specifically "durvA arthe/artham udakam samarpayAmi" (I'm offering water in place of DurvA).
Some people also offer akshatas (unbroken riced mixed with a little of turmeric) in place whatever UpachAra that is missing but I don't have any scriptural support for that practice.
The book "Nitya Karma PujA PrakAsh (Gita Press)" (p 297) also states that when any particular ingredient is missing from the PujA, akshata (unbroken rice grains), flowers or water can be offered. Or one can also mentally imagine to be offering those ingredients.
In the image above, in the option (Ka), it is stated that one can mentally imagine to be offering the ingredient (in your case DurvA grass) when it is actually absent.
The option (Kha) states, that in such cases, one can offer akshatas, flowers or simply water in place of the missing ingredient.