I did notice some days ago this note on PrayTell about a shortage of palms in New Orleans.
Because of the deep freeze that hit hard this January, palms that are typically plentiful in New Orleans are now in short supply.
Instead of the usual queen palms which were killed in the freeze, it has been recommended that parishes use sago palms, which are brown and much skinnier than what Catholics are used to seeing on Palm Sunday.
The Directory on Popular Piety and the Liturgy suggests olive branches. or even “other greenery” as a Palm Sunday choice:
The faithful usually keep palm or olive branches, or other greenery which have been blessed on Palm Sunday in their homes or in their work places. (#139)
I once encountered immigrants from Poland who bundled dried flowers and branches and had brought them from home. It was their tradition, they said.
Freeze or not, I suppose any plant branch with green on it will do, right? Anybody see anything other than palms this weekend?
Catholic Sensibility 
FWIW, Queen Palm leaves transport well (if anything, they are marginally invasive, and their very edible berries are not much of a commercial crop so far as I am aware); I don’t think that olive branches do, and there likely are far more palms in the Americas than olive trees, which have a much more restricted biome.
Willows would probably work better; indeed Salix purpurea (purple willow) is almost too easy to cultivate where there’s somewhat moist oil, and when coppiced annually, is a basic for traditional basketry; moreover, willow is one of the four traditional branches of Sukkot.
Some Eastern Europeans use pussy willows in place of palms.
Here in Honduras, there are at least two different types of palms but people also have bouquets of palms with other flowers.