Is samsara without end? I read the following in the PTS Pali dictionary: 


  Saṃsāra "whose beginning and end are alike unthinkable", i. e., without beginning or end.


Are there any Pali suttas that support this view of endless samsara without an end?
Well, from Mahayana perspective it's both. Samsara is endless, just like Dukkha is an invariant principle of sentient existence. Accepting Dukkha (here, inherent unreliability) of phenomena makes it Tathata, suchness. Accepting Samsara makes it Nirvana. Does not mean Samsara has ended or Dukkha ended - not at all. We just make an end to it (nirodha, 3rd N.T.). Endlessness of Samsara is one thing you can truly rely on, which makes it unconditional Nirvana.

Now, if I forget all that and just reason from the original sources, here is what I get:

Looking at your PTS dictionary quote, they are talking about Anamatagga (without beginning / without end) being an epithet of Samsara. When I search Sutta Central for "anamatagga" I find for example this verse from Therigatha:


  "...Long are the foolish in Samsara,
  again and again cry
  without beginning, without end, over the father's death,
  the slaughter of the brother and the murder of the self.  
  
  Oh tears, breast milk and blood:
  without beginning, without end you run in Samsara!
  Remember the wanderings of the creatures
  and the way the bones pile up! 
  
  Remember the four oceans,
  filled with tears, mother's milk and blood!
  Remember in one epoch
  bones heap up like mount Vepulla!  
  
  Without beginning, without end have you flowed (lit. samsara’ed),
  endless like the seeds of jujube fruit. ..."


This, combined with the literal meaning of the word "samsara" - "running by itself", "drifting" can point us in the right direction. Samsara is endless unless we put an end to it (nirodha). And how do we put an end to it? By applying the principle of this/that-conditionality and undoing the 2nd noble truth, i.e. by accepting what is and arriving at tathata. Now technically, what we accept is not really Samsara as it is, that would be surrendering. Instead, we learn to see Shunyata and that's what we accept, Samsara-as-Shunyata. Does not mean that Samsara has gone anywhere though, it is still endless as it always were. In fact, if we want to help other sentiment beings, we have to deal with Samsara every day.